"Sometimes she would wake me up in the middle of the night. It gave me heavy boots that she had nightmares, because I didn't know what she was dreaming about and there was nothing I could do to help her. She hollered, which woke me up, obviously, so my sleep depended on her sleep, and when I told her, "No bad dreams," I was talking about her." (104)
I think Oskar has trouble sleeping because he thinks that if he sleeps he will miss a clue that his father left behind for him
Oskar is always inventing new things when he has trouble sleeping. I think inventions and trouble sleeping are somehow connected to each other.