Has anyone here torn a muscle? What does it feel like?

When I am at the gym and i do preacher curls it feels like my forearm is separating from the bone. I have an extremely high pain tolerance and sometimes i cant take it and i have to set down the weight. I didn't used to have this problem with preacher curls until i started doing straight bar curls. I havent touched preachers in a few months, just been doing hammers, straight bar, and concentrations. The "tearing" feeling comes along the bone. I dont exactly have large forearms either, i have that small wrist look i guess. Any insight? I'm not about to make a special trip to the docs either, my doc is a ****in retard. If someone could help me out i'd appreciate it.

Frost