Hi, one possibility is that the local anaesthetic (which contains epinephrine, aka adrenaline) was accidentally injected into a vein instead of muscle tissue. This can cause a very dramatic increase in heart rate. While not dangerous, such an experience can certainly be unsettling, but the chances of it happening again are extremely slim.
It is more likely though that you were experiencing anxiety. Symptoms like:
- a racing heart
- shaking uncontrollably
- breaking out in a cold sweat
- not being able to breathe properly (breathing rapidly/hyperventilating), leading to dizziness, lightheadedness and tingling in fingers, toes and lips
are all signs of an adrenaline rush - but it's unlikely that the epinephrine in the injection caused it. The amount of epi in local anesthetics is tiny compared to the amount your body naturally pumps out.
Either scenario is not dangerous, but a panic attack can be very disconcerting - especially when you weren't expecting it and it takes you by surprise. Panic does not pose any danger - our bodies are made to deal with adrenaline surges and indeed, they're designed to keep us safe from danger (that's why it's called the "fight or flight" reaction). It is a built-in response which has evolved to help us deal with enemies such as dangerous animals. It would be more accurate to call it the flight, fight or freeze reaction (when confronted with a big but slow animal, you'd be inclined to run away, when confronted with an animal that's about as strong or weaker than you, but faster, you may decide to fight, but if the animal is bigger, stronger and faster than you, then freezing would be the best response, in the hope that its eyesight may not be good enough to track you down).
In today's "civilised" world, there's little need for the fight/flight/freeze response, but because it's such a basic mechanism of survival, it's easily triggered by things that frighten us. Maybe part of the reason why you didn't let your dentist know was that you were caught up in the "freeze" response.