Literally what I thought when I saw that. When he didn't move in the next frame, I thought he had pulled something amd was going to ask her to help him to the couch.
Chapter before she was drunk on coffee and now he is covered in bruises, replacing the bed frame and realizing she is pretty heavy (not fat, just a lot of mass), the night must've been freaking wild...
From what I understand, it's because she's actually much bigger (= more weight) than her human form would imply, so she's effectively denser than the equivalent human body?
Science dictates that matter can't be created or destroyed(only transferred or transmuted, like into energy or something)...so her smaller human form would have to be denser than a normal human. If that's what the author going for here...