Re: I wake up in the middle of the night because...
My almost 3 y/o DD was screaming in her sleep last night right about the same time, 3:45am. I went in her room and she had slid off the bed and had her feet on the ground and her head on the middle of the bed. I asked her if she wanted to go potty and she did. Then she went right back to bed.
Sometimes I think she has to wake up to pee and then falls asleep before she makes it out of her room, but still has to pee, so doesn't go back to bed comfortably (she wears a pull up at night and wakes up dry 75% of the time). I've found her asleep on the floor in the hallway outside of the bathroom before too!