What you're experiencing is the "Tetris Effect". After doing something repetitive for a prolonged period - whether it be something work-related or playing a video game - you'll start to see it whenever you close your eyes, and you'll especially see it in your HI.

I'd suggest playing Tetris for a few hours straight before going to bed. I've never actually done it myself, but my hypothesis would be that focusing on the falling tetrominoes you'll inevitably see after closing your eyes will help keep your mind awake enough for a WILD.