We have a new behavior to report.
All we can figure is that someone is slipping Sydney some delayed release crack at school. When we get near bed time, rather than laying down or acting as if she can't hold her head up, Sydney is snapping into this super energized mode where she's just nuts. She runs from room to room, jumps up an down, screams (happily), and just keeps going. The first night this happened, she escaped wearing only her diaper. The second night she managed to escape without even the diaper. We literally had a crazy naked toddler sprinting around the house yelling with a big ol silly grin on her face.