In the past, when I had dental work done (fillings, etc.) whenever I had a shot of Novocain, I would immediately feel like I was having an insulin reaction. Turns out, they often mix adrenaline (epinephrine) with the Novocain (it makes the anaesthetic work faster & longer).
I have had them note this on my chart, and now they use Novocain without epinephrine added. If you are having the issues I was, you may want to talk to your dentist about it.