Sorry to necro this thread, But I've noticed that my vampire sims don't like to sleep in their coffins for very long, they'll stay in there for maybe half a sim hour before waking back up before heading off to do something else. Even if I send them to their coffins with nearly depleted energy bar's they'll only sleep long enough for it to become half full before waking up again. Yet they sleep in a normal bed just fine, which is ok, unless a vampire sim has the restless sleeper weakness, then it's just annoying... :-/