How old is your mattress? Maybe you need a replacement, or a different kind of mattress. It's amazing what a change can do! Also, if specific parts are stiff, you may be able to figure out some specific "fixes": ie: stiff neck= different type of pillow, or avoiding sleeping on your stomach (which is the worst possible position for getting everything out of whack!); stiff lower back = sleep with some pillows under your knees (I do this, and have told others with lower back stiffness to do so, and it works wonders); stiff shoulders/elbows = be aware of your sleeping position (ie: are you sleeping in some contorted position that puts stress on these areas. I know it's hard to change the way you sleep, but I used to sleep with my arm slung over my head --and had done so for years--until I read that this may actually contribute to impingement problems. Since then, I've modified my position, putting a pillow next to my elbow and bending my arm up so that only my hand is over my eyes--what can I say, I was a cat in a previous life and need eye coverage at night!--and have noticed much less stiffness in my shoulders).
I am no way, no how, not by any means possible a morning exerciser, but some other things you can do (and which may have been mentioned) are: stretch well before going to bed (making sure you are warmed up, either from a warm/hot shower or bath or some light cardio warm-up; get a heated mattress pad so that your muscles are warm in bed; take about 10-15 minutes to gradually transition from bed to full-out up, by doing some gentle stretching and rythmic mouvements, first lying in bed, then seated, then standing.
