Like 3 or 4 times a week for the past 5 years, either right before I go to bed or when I wake up in the middle of the night to check the clock and try to go back to sleep, something like a film strip of images moves by really fast and so fast that I can't see the images. I then start to shake uncontrolablly and, the longer I keep my eyes closed the worse the shaking gets and the faster the images rush by.

Any idea what's happening??