I have a molar that is doing the same thing - very sensitive to cold & heat and it already has a filling in it. Last visit to the dentist confirmed that the tooth has tiny cracks. I am putting a floride gel on every night, but it is not helping. My dentist knows how much I hate to have dental work done and so was hoping that the floride gel would help. I brush with warm water and try and keep the tooth as clean as possible until I can get an app't to get the thing capped. I don't want to wait too long or else it will turn into a root canal. Its the worser (is that a word?) of two evils.. get a cap or get a root canal. I'm thinking the cap will be less uncomfortable.

Keep taking deep breaths and call your dentist. Is there a friend who can go with you ?? Knowing a friend is waiting for you in the waiting room might help. And who knows, maybe just the filling has a leak - which means the tooth needs refilling but is not as intense as a cap or root canal.

Make an app't as soon as you can. Usually, the dentist looks at the situation firsts and then if work is needed, you have to come back. Go and find out. I'm thinking that finding out for sure will relieve some anxiety. Its the not knowing that is tough to tame.

Good luck and I hope it turns out OK for you.