I don't know what your nightswimming dream is exactly, but the title and the picture remind me of a nightmare I often had as a child - something fell on me, like a crane, and I wanted to run away but I couldn't as my feet wouldn't move. Never found out how it went on, as I woke up before the final crash.
So unlike some commenters I don't miss the nightmare idea in this one at all, I think it communicates the idea quite well - at least to me.