I swear, this happens to me all the time if Im really seriously drawing (where its halfass decent). Or if Im not having to fight to get down what Im seeing. But if I keep at it, I get night terrors from lucid dreaming. The sensation of drawing feels great, and its the only reason I do it, but then when I go to sleep, this shit happens and I feel exhausted the next day even if I slept alot..... Happened all the time as a kid.