I'm 100% not joking, I once was stuck the the proof of a theorem for a whole week going at it and still wasn't able to prove it... until I dreamed of the solution, woke up at like 3 am, quickly wrote a skecth of my dream's proof and went back to sleep. The following morning I checked that path and boom, there it finally was the solution.
Weirdly enough, this happened twice, although that second time I didn't woke up at 3 am, just in the following morning as usual.