ToME: the Tales of Maj'Eyal

I should be able to kill them, execution style, if there are no other enemies around. It's pretty easy for a character to walk up to a sleeping monster and slit its throat...

Bad idea. Talents and effects, in this game, are pretty much always symmetrical. What would you think if you walked around a corner and instantly died because something slept you and then something else executed you?

Monsters are already passive. They very rarely open doors. They rarely roam the level. Sit in a corner and rest - in 95% cases nothing will come to you.