I experience inappropriate amounts of guilt. How do I get over this?

Practically everything makes me feel intense guilt. Anything less than perfect grades, not doing something my friends or family ask me to do (even when it’s practically impossible or would put me at great disadvantage), feeling as if I haven’t accomplished enough, both in a given day and in my lifetime, etc.

This guilt makes me sick to my stomach, and not be able to sleep. I spend hours agonizing over my decisions, replaying conversations, and reasoning with myself. I feel like a terrible person and a failure the majority of the time.

What do I do?