I fought the sorceress in Sancaster, and now my sorceror dies every time I rest. I've healed him, raised him from the dead, everything I can think of. Any idea what is going on?

Which game?
How old is your sorceror?

Worlds of Xeen and I think he was 44.

What's his endurance ?

Does being cursed cause a character to die? Check if he is cursed (and check for any other condition at the character screen).