The result is a nasty case of bursitis, which then gets worse every time it twinges (like when you roll over on it in bed).
Ugh...I recently had bursitis in my left shoulder. Seems like it resulted from good ol' fashioned overuse, not from any one particular incident. Took about two weeks for the pain to go away completely, and another 2-3 weeks for the rest of the soreness to recede.
Seriously, though...shoulder injuries majorly suck - even minor ones. Mark, if you are losing mobility in your arms, definitely see a doctor (or better yet, a physical therapist) ASAP. Definitely don't want any possible injuries to get any worse!