I think the baby moves other parts of the day also you just feel it when you are laying down/relaxing more because your mind isn't doing other things.
Lol it seems like it would be the opposite. But that makes sense.
Its a natural thing they all do. When your w up and moving throughout the day we rock our babies to sleep then at night when we aren't moving as much they start getting active.
My dad told me that when you're up moving around the movement of the fluid they live in rocks them to sleep and when you relax they wake up and get to moving about. Made sense to me so that's what I think it is (: