Ideas
My Sims are constantly waking up in the middle of the night for no reason, along with them often times refusing to go to bed when there is someone else in bed, causing their partner sim to get up when they get into bed, or their partner sim to getting up whenever they get up, no matter what the sleep need is. This has made it very difficult for my Sims to get a full night's rest before work in the morning. They are not waking up to a baby, animal, or any other kind of noise. I would assume it has to do with the cuddling mechanic in Lovestruck as this never happened before I got the pack and it mostly is happening when there are two Sims in a bed, though I had a toddler get up multiple times without being fully rested as well.
Because of the other issues with sims waking up if their partner gets in and out of bed, it makes them getting up in the middle of the night all the more difficult because they will often immediately reawaken or refuse to go to bed.
The toddler one might not be related. I'm not sure. That has only happened one night, though it was multiple times in one night. I should note that though Lovestruck was the first pack that came to mind that would be causing this, I had downloaded multiple other packs around the same time after receiving many gift cards for Christmas. I can't remember all of them, but it was a lot. I think it was Lovestruck, Life and Death, Horse Ranch, maybe Eco Lifestyle and/or Island Living, Outdoor Retreat and Dream Home Decorator, Toddler Stuff, Moschino, Tiny Living, and maybe Laundry Day. However, I don't see any of them affecting this other than Lovestruck, though I could be wrong.