Sims keep getting out of bed

Lately whenever I have 2 sims sleeping in the same bed, the last one who goes to bed doesn't stay asleep. They get out of bed after only a few seconds. I have to direct them to get back into bed and then they finally stay in bed and go to sleep. 

This isn't just one household, it's all sims. Most of them are married with 100% romance and friendship, and there is no TV, stereo, or other disturbance in the room.