Peter,

something similar happened to me. I got hit on the back of my head, and was diagnosed with PCS. That was december, last year. 6 months in, work comp released me, and my medications ran out with no new script. W/in 30 days of running out of meds, I got a terrible pain in my neck followed by facial drooping. The emergency room ruled it Bells and prescribed a run of steroids. I actually had to get two runs of steroids before it went away for good.

If half of your face is drooping, then either your 7th or 8th nerve is being pinched or in other ways compromised. That does not go away on it's own, usually. I would seek medical help for it. I don't think it can go away on it's own, and I'm pretty certain it can get worse.

Good Luck