Why could i pass out 5 minutes after getting a novocaine shot at the dentist?

Syncope: Here is more information on fainting than I can fit into this small space: http://en.wikipedia.org/wiki/Syncope_%28medicine%29 A medical history, physical examination, and electrocardiogram (ECG) are the most effective ways to figure out the underlying cause. You'll have to see a local physician to figure out exactly why.

Vasovagal syncope: It is also known commonly as fainting. This is quite common. At your next visit, you should ask your dentist to use a local anesthetic that does not contain epinephrine.

Many variables: Every dentist is prepared for a nervous patient that may faint/ syncope. What are the variables? Did your MD state that you can only have carbocaine? Are you sensitive to epinephrine? Did you eat prior to the appointment? It may be a good idea to have a mild oral sedative to alleviate anxiety, be sure to bring a driver.