I've found that my ability to get comfortable is directly related to my eating and exercise habits. If I eat heavy or unhealthy foods for awhile, and get less exercise than I'm used to, it's manifested in achy, annoying, discomfort. When I've been diligent in my exercise (yoga particularly), I am able to get comfortable more quickly and easily -- in a bed or chair.
Same for me here. I tend to be kinda tense, but exercise helps me a lot to relax. Great for stress relief also.
