I understand what you were going for with this flash. The only problem is, it didn't work very well because of the way you executed it. This could work very well as a storyboard or an animatic, and the only complaints I have for this one is the way in which you chose to execute it.
For instance, it wasn't clear what that first shot you drew was. When he was sleeping, you could've had a dark background and have it fade to black for effect and to give off a "nightmarish" vibe. You should've extended the part with him falling, that's one of the most important shots in something like this.
Him falling could've been done better. When you fall, you start off kinda slow and get faster and faster; you accelerate. Also, instead of showing him open his eyes, you should've timed it so at the right time, it just cut to his eyes, and then show "FIN" for a short period of time.
Just some suggestions. 3/5