Sit back and breathe. It's going to be OK. Don't listen to the horror stories! You don't want to get the teeth cut out, especially if they're molars, because without molars, you can't chew. Also, missing teeth affect the positioning of all your other teeth. Keep your teeth! You'll be fine.
I have had nine root canals and they really aren't that bad. It's kind of like getting a filling, but there's a little more pressure and it takes more time. The dentist will use novocaine like he does with a filling, so you will be numb for the procedure. Also, if you are very anxious, you might want to ask for gas. (nitrous oxide) It's great stuff. It really takes the edge off the anxiety. You kind of feel like you are floating and don't really care what's going on.
Hmmm. The breathing thing. I really don't know what to tell you there, I'm sorry. All the best to you.