My textured ceiling usually looks like it's breathing and swirling a little when I'm on my back catching my breath after a vigorous bike ride.

Had a friend who would get tracers while working his back muscles at the gym.

Honestly I'm not sure how much is a flashback vs having the previous experience of tripping to notice little things like the ceiling breathing. It's subtle. Maybe everyone's brains do that, and people who haven't tripped before just aren't primed to recognize it?