Recently (I think since I installed ambitions but I'm not 100% sure) I've had 3 sims (all in different games) pass out for no reason, with reasonably full mood bars and no negative moodlets.
On all 3 occasions I looked for some indicator of why they would pass out, but each time they have been in the middle of a mundane, harmless task with nothing negative going on. One sim was washing his hands, another was watching tv, not sure about the third. Each one stopped what they were doing and had an action that said 'pass out' when I cursored over it. I couldn't cancel the action, I just had to wait for them to pass out and then wake them up.
Anyone know why this is happening?