I saw my GP for this about 3 years ago because every morning I was actually in considerable pain, unable to straighten my back, and my neck and shoulders were stiff - you know when you sleep awkwardly and wake up with a stiff neck? That sort of feeling, only it didn't really ease at all.
My doc thought I might have PMR (polymyalgia rheumatica) and arranged some blood tests. He was right, and prescribed steroids - 15mg a day - and within 36 hours I was pain free. I could get out of bed each morning and stand up straight, it was like a miracle!
He told me that the condition often disappears after about two years, with treatment, and no-one knows why this is.
The idea was to gradually reduce the dose, 1mg at a time. I'm afraid I have been nervous of this, which is why I've gone on taking the stuff for longer. However, I'm now down to 1mg a day and hope to give up altogether in about 2 weeks. I am a little stiff now in the mornings, but nothing like I was before.
So if you're very stiff and bent in the mornings, with neck, shoulder and maybe hip pain, and this wears off within a couple of hours, it might be worth seeing your GP - it could be PMR.