I Passed Out at the Dentist. Why?

As a full time general dentist in private practice, I’ve seen patients faint more than once. And as a dental blogger, I’ve seen all types of comments and questions on this site about patients passing out. In fact, most people mistakenly assume that when something like this happens, it is because they are allergic to something the dentist used. In nearly all cases, that is an incorrect conclusion.

So, why is it that some people faint and/or pass out at the dentist? And what causes it?

Common Medical Emergencies in Dental Offices

In a widely cited survey, the number one emergency seen in a dental office is fainting – or more appropriately called syncope (sources: here and here). In fact, in one study, syncope accounted for 53% of all emergencies in a dental office (source: here). The second most common emergency is hyperventilation.

fainting at the dentist is not treated as an allergic reaction

Many mistakenly assume that fainting at the dentist is due to an allergic reaction.

To many individuals who’ve had adverse reactions at the dentist, this fact can come as quite a surprise. The scenarios that most patients believe are occurring – usually acute allergic reactions as well as cardiac events – very rarely occur.

Fainting vs. Passing Out vs. Vasovagal Syncope

Generally speaking, the above three terms are all roughly the same, with the term vasovagal syncope being the medically appropriate one. It can be defined as a temporary loss of consciousness due to a decrease in blood flow to the brain.

dental needle fear can cause fainting or passing out.

This is the most common trigger for an episode in a dental office.

Your brain is in constant need of oxygen. If blood flow to the brain is temporarily diminished, you are no longer able to function, and you lose consciousness. If this happens, it most often results in you falling to the floor, which then puts your head at the same level as your heart. This change in position, along with the removal of the stimulus which caused the episode (more on this later), then allows for adequate blood to flow to your brain, and you very quickly regain consciousness.

In vasovagal syncope, a trigger (such as the sight of a needle) will cause a susceptible individual’s nervous system to over-react and cause certain physiologic changes which can lead to the decrease in blood flow to the brain.

Common Triggers of Vasovagal Syncope in a Dental Office

dental drill can cause you to pass out or faint

The dental handpiece or “drill” can cause some to pass out.

A dental office is a unique setting in that the patients walking through the door typically don’t want to be in the office, but they know they have to. This is why passing out episodes occur quite frequently. The most common triggers seen in a dental office include:

  • The sight of the needle (this is the number 1 trigger).
  • The slight sting of the dental injection.
  • The sight of blood.
  • The smell of an office.
  • The high pitched squeal of the dental handpiece.
  • And others.

So, if a trigger is experienced by a susceptible individual, the syncope episode can commence.

A Typical Fainting Episode at the Dentist

Each and every episode of passing out is unique, as is every patient. The following is a classic example of what someone might experience in a vasovagal syncopal episode at the dentist.

  • You don’t like coming to the dentist but you know you have to get a filling. You have been dreading it for over a week.
  • You are called in from the reception area. While walking in, you see a needle that looks large and intimidating.
  • The dentist comes in and says hello. At this point, you’re still thinking about the needle, and you begin to feel somewhat lightheaded.
  • You hear the dentist talking to the assistant but their voices seem muffled. You notice that you are breaking out into a sweat, even though the temperature was perfect just a couple of minutes earlier.
  • You begin to have a feeling of nausea and your thoughts appear fuzzy. Your muscles suddenly feel incredibly weak and you don’t even think you could lift your hand. You attempt to say something but you can’t muster the strength or thoughts to put words together.
  • Your vision appears compromised, first by seeing bright lights, and then with black or cloudy vision. You are sitting upright but all you want to do is lie down…

Next thing you know, the chair is completely reclined and you are lying horizontally in it. The dentist and the assistant are sitting next to you. The dentist is looking at you intently and is feeling your pulse on your wrist. He/she notices you waking up and says:

“Well, it looks like you fainted for a bit. Don’t worry. It happens more often than you think. We’ll keep you reclined for a couple of more minutes and then we’ll slowly bring the chair up.”

Final Thoughts

If this is anything like similar posts, this will generate a lot of traffic and comments. Please consider reading other posts I have on similar topics. If you think you’re allergic to novocaine, you should read this three part series (one, two, and three). If you think you’re allergic to epinephrine, you need to read this and this. If you’ve had difficulty getting numb, check out this post and this post. Enjoy!



  1. I passed out because the numbing meds went into an artery! I constantly have swelling, soreness, mouth sores, etc because Dentist use acrylic in various items, which I am highly allergic too, even after I have grilled them on the fact it cannot be used on me! Temporary plate and temporary crowns are made of allergic! The pain and has missed time from work have mounted up! One dentist said start steroids, and benadryl before you come in.

    • Suzanne,

      You indicate that you passed out after an injection went into an artery. I do not know your medical history nor the medications that you take. Nor was I there for the incident. Injection into an artery is more properly called an intravascular injection. This is an unintentional adverse reaction that occurs to all dentists, regardless of the precautions they take.

      Why you passed out is not know. However, intravascular injections can be a trigger for vasovagal syncope. So, you may have inadvertently proved the point of this blog post.

      Regarding your acrylic allergy, I don’t know how that is relevant to this blog post.

  2. Stephen Rowe, DMD. says

    Great article; also see syncope commonly in hypoglycemics which notoriously don’t eat before appointments.

  3. Hello… just want to ask if the dentist can still proceed with the procedure even after the patient have had fainted and gain consciousness?

    • Mark,
      This is really a case by case basis. A lot of it comes down to WHY a patient faints in the first place. Fainting of a diabetic due to hypoglycemia – probably not a good idea to continue treating that day. Fainting of an otherwise healthy patient due to nerves (vasovagal syncope) is less of a concern and treatment that same day could be considered.

      • THANKS! This answer is exactly the reason I came here. I’m generally certain I will pass out, but I walkouts like to be able to continue the procedure, instead of having all parties give up for that day, only to postpone things.

  4. while in dental chair lying down getting permanent veneers I started to yawn a lot and the got very tired and had a few fast spasms in my face and arms. I apparently wasn’t breathing deeply enough …. closed my eyes and dentist loudly told me to breath and I went to lift my head and was VERY dizzy for 10 seconds or so. He had me take deep breaths and lifted my legs and said it was slight reaction to lidocaine and all was well … after making me drink and breath deeply he did two more hours work without incident but im a little worried to go back for the rest of the work now??? Thoughts

    • Carol,
      I was not there but everything you describe – including the dentist’s reactions – are consistent with vasovagal syncope.

    • thanks so much dr. calcaterra
      is vasovagal syncope always related to anxiety because I wasn’t and never have been anxious at dentist

      • There are many “triggers” for vasovagal syncope. Anxiety from the dental procedure can be a huge trigger. Sometimes the trigger is harder to pinpoint. I had one patient experience it when he saw our x-ray machine which was somewhat similar in appearance to an x-ray machine that he once had to take his elderly mother to. For him, the image brought back painful memories, and he experienced syncope, resulting in loss of consciousness for nearly 10 seconds.

  5. John fake name says

    Happened to me today. Had to get rid of my wisdom teeth. The Doc injects anaesthesia in two zones of my gum. After around 5 seconds I feel the typical pre-fainting feeling but I didn’t expect it so I’m asking the Doc if should fall asleep after the injection and I hear no response because I blacked out. Next thing I remember is how I slowly open my eyes and see water “flying” towards my face and I feel a strong smell (a special kind of spirit used for those who pass out, they pass it by your nose and it’s so bad it wakes you up, simply speaking). Later the Doc said I’ve been out without breathing for around 15 seconds. My blood pressure got checked and it’s low but got to normal in around 15 minutes. I still felt week and dizzy but generally I was okay. The Doc decided not to pull out the teeth and leave it for another day.

    • All this time I was laying on the chair in almost horizontal position.
    • I am not allergic to anaesthesia.
    • This is the second time I’ve ever passed out.
    • I’m not a fan of injections in general but not that I’m afraid of them. Had enough injections before.
    • In general I’m in good health condition and don’t have any kind of phobias.
    • I’m male 25 y.o.

  6. This happens to me after injections because I have low blood pressure (dysautonomia and post orthostatic tacyhcardia syndrome: mostly harmless but very bothersome condition). I just had an oral surgery and I was fine the whole procedure until I went to sit up after and immediately fainted. I’m not nervous at all of needles, dental work, or medical procedures and am pretty “tough” with pain and illness, so it really surprised me that it happened again this time. I also fainted twice the next morning – though I’m not sure why it happened that long after. For me, I start to get nauseous, my breathing and heart start racing, then I feel dizzy and can’t balance, then a loud rushing noise starts blocking out other sounds, I feel overheated, my stomach feels achy, then my vision spins and goes blurry, all my muscles go limp, and then blackness. When I come to, it’s like rushing through a tunnel as the noise clears, then I feel extremely cold and usually get the shakes. Very classic syncope!! Cold juice sometimes really helps, as does lifting your legs.

    I have random fainting episodes normally so I’m not worried. Low blood pressure is often considered not clinically significant but it’s something to monitor due to reactions such as this, and if you have it, it can be helpful to tell all your doctors and dentists. 🙂 Then they can keep an eye on you. I’ve fallen off a hospital bed before. My hygienist once told me off for not mentioning it lol.

  7. I had a full mouth extraction for dentures. ( 19 teeth )
    Immediately after I felt really warm, then they said I passed out. I didn’t think so as I heard the assistant talking. My blood pressure dropped to the point where they could not get a reading. My dentist said I bled more then anyone she has operated on.
    I had to go to hospital where they gave me 3 bags of fluid to get my blood pressure up.
    I threw up at least a bag full of blood I had swallowed during treatment. What caused my pressure to drop from normal to nothing and why did my teeth bleed so much? I’m not on any type of medication

  8. I have ‘passed out’ at last two dental procedures. I fall into deep sleep, and I think it’s combination of anxiety, coupled with laying flat. This article helped me to understand it better!!!

  9. Today I had a biopsy completed and the procedure only required local “freezing.” Although I HATE needles, I never expected to pass out. Strangely, I made it thru the entire procedure, but for me what triggered my hysteria (my mind began racing) when I could taste the blood in my mouth and run down my throat along with hearing the dentist tell his assistant where to place pressure and where to wipe up the blood. Then the stiching began – I didn’t like that. Even though I couldn’t feel anything I could picture what they were doing… once the assistant said to me they were all done, is when I dropped… sweats, dizziness, nausea.. I thought I was dying! Lol they put oxygen up my nose and gave me juice to drink.. it felt like forever before they gave me those things – but I immediately felt better. (It may have taken 5min) Although scary at that moment- I felt so embarrassed afterwards‍♀️ here I am a grown woman, have delivered two children with no problem, yet couldn’t do an oral biopsy!

    • I was not there for the procedure. But your description fits vasovagal syncope perfectly. The key is to recognize it so that you can hopefully avoid situations like this in the future and/or reduce the likelihood of it happening if you are going to be in that situation.

  10. This happened to me 2 times in a row, the first time a week ago, and the second time was today. I’m getting dental crowns so the dentist is extracting teeth that cannot be saved. I’ve had local anesthesia a lot of times, not just for extractions but also for other dental work and this has never happened to me. I’m not an anxious person, I’m not afraid of needles at all. Just 3 weeks ago I got 5 teeth pulled out on both sides on my upper jaw, which means that I was injected two times and I didn’t had a problem. But the last two appointments the extractions were on the lower jaw. The first episode I immediately felt weakness in my legs, followed by heaviness in my head, the dentist noticed me I wasn’t ok and he reacted in time and I did not faint. The second time around, the first reaction was pounding of my heart and tachycardia, followed by tremor in my arms. Both times the symptoms started a few seconds after the administration of the anesthesia, and both times the anesthesia didn’t work and they had to administer a second round. Both times they injected me again after the episode, and both times after the second injection I was ok and they pulled out my teeth without a problem. I’m really confused, because as I said, I really am not afraid of needles and I’m not an anxious person, yet this happened to me two times in a row, and both times the reaction blocked the anesthesia and I didn’t numb. On a side note, is it normal for the cheek, ear and even part of the head be numb after the administration of the anesthesia?

    • Sanja,
      I was not there for the 2 incidences. However, your description matches that of vasovagal syncope. The “trigger” causing the episode could be the anticipation of the needle, the actual insertion of the needle, or some small amount of local anesthesia entering your circulation. The fact that you recovered so quickly also supports the syncope case. And depending upon the location of the injection, the ear/cheek/head can also get numb.

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