I'm 100% certain I know what's causing this now. The sims only run to the center of the bedroom when Larry's in bed. Furthermore, despite what I'd originally thought, Larry never displays this behavior. During the day, the other household members and any guests will leave what they're doing, go wherever Larry is located and display a number of autonomous actions. This may go on for an hour before the sim resumes what he or she was doing. The only time I can guarantee it won't happen is when Larry's not at home. Given the nature of the actions, I'm confident this is related to Larry's daredevil trait. It's as if he's performing a daredevil action, like eating a bug, and the other sims are reacting, only Larry's not doing anything at all. He's sleeping, or writing a novel, or cooking. I've never been a fan of the autonomous and repetitive self-directed actions (OMG, the toilet won't flush!), but this is a new level of annoying. I've got two and a half weeks left in the challenge, so I'm sticking it out, but my god, how bothersome!