I have had a shoulder injury in the past that never healed. Nothing heals when you have a connective tissue disorder. However, one thing I've found exacerbates the shoulder pain is how I sleep. I have to be very aware of my sleeping position, otherwise I will end up with all sorts of extra pain the next day.
If I'm off the anti-inflammatories and muscle relaxers, I also sometimes will wear my thumb splints at night, because they'll compress my hands and wrists, decreasing the chance that I'll clench my hands/fists in my sleep. I've found that having a soft to medium pillow or two will provide a little support for my head, while I position it so my shoulder can rest without being compressed, and that seems to alleviate some of the shoulder pain.