Folks tend to assume the same sleeping postures because of comfort.
This can cause tissues to creep (adapt to prolonged stretching) which can result in stretch weakness. For instance, side sleeping without a pillow between the knees can promote hip weakness from prolonged stretch of the gluteus medius. Lower trap and rhomboid can also be overstretched depending shoulder positioning while on the side.
Folks that sleep with pillows under their knees promote shortening of the hip flexors. Comfy for sleep, bad when it comes time to stand upright.
These are difficult to address because, of course, you're asleep most of the time.
Bill