My dd's daily routine is pretty straightforward. Before she started the night wakings (last Friday), she woke up about 7 am, had breakfast, played and we would run errands or whatever. She eats lunch at 11:30, we leave at noon to pick up her big sister from preschool, and we're back home at about 1pm. Then she takes a nap (typically an hour and half to two hours), then she's up, has a snack and plays for a few hours until dinner at about 5:00 or 5:30. Bathtime is 6:30, with bedtime between 7 and 7:30. It's been a fabulous schedule since about June and didn't fall apart until last week.
The only thing I can think of is separation anxiety. Sometimes on the drive home from preschool she falls asleep in the car and then I put her in her crib to finish the nap ... maybe that's freaking her out or she is losing her fall-asleep alone skills? She seems to wake up happy from naps.
I tried the technique of laying her down every time she stands up and that worked okay ... except it took about an hour to get her back to sleep at 3 am, and she was up again at 5 and 6:30. She seems to listen for when I leave the room and screams as soon as she hears me leave, even when I think she's asleep.
I'm getting sooooo tired... no chance for a nap since I have another one!