My tooth feels warm, do I need a root canal?

I have a cavity in my lower left second molar, but I am going to the dentist on Thursday, in the past week it has started to feel warm sometimes, but not all of the time, I wouldn't call it painful but I'm aware that it is there when I think about it, will this need a root canal? I have a dental phobia, I can handle fillings but the though of a root canal scares the life out of me, would it be easier to have the tooth extracted? Or am I just whittling about nothing and I'll require a filling?