You’re certainly not alone. The cause may be bursitis and this can occur either with the hip/leg on top, or the one that is pressured against the mattress. Hip bursitis can either be acute or chronic hip bursitis.
WHAT IS BURSITIS? Bursitis is dysfunction in the fluid-filled sac (bursa) that normally provides buffering and lubrication for tendons gliding over a joint. It is often caused by new or old injuries or can be a result of lack of important nutrients to the joint. Acute Bursitis is inflammation of the sac and perhaps over-production of fluid (swelling). Chronic bursitis actually presents with dryness, lack of fluid and poor lubrication for movement of tendons.
HIP PAIN ON THE DOWNSIDE Although there are many facets of treatment and self-care for bursitis of the hip joint, a pressure point relieving, supportive foam mattress is one very important aspect of treating it. REASONING: (1) It is important to not have pressure on the inflammed bursa while lying on that side. (2) Additional to excessive pressure, poor mattresses lack support and often sag or hammock. That places an undesirable stretch on the muscles associated with the hip on the downside, thus irritating the bursa and impeding healing. One might wake up with pain, clicking, stiffness and limited mobility which may lessen after being up and about for awhile.
HIP PAIN ON THE UPSIDE Alternatively, your pain may occur in the hip that faces upward. I know this seems sort of odd, but it is actually quite common. REASONING: (1) In most people, their hips are wider apart than their knees. This is especially true in women. This anatomical truth can create tension on hip muscles as the knees come together and stretch such muscles. (2) Or perhaps, one stretches their leg out in front of them twisting the spine and pulling on hip muscles. In those with bursitis, this can wreck havoc with the sensitive bursa. (3) Of course, a supportive, pressure relieving mattress is advisable to prevent excessive hip rotation.(4) However, in this case it is often advisable to also utilize a nice space occupying pillow between the knees. The pillow should be soft enough to not impede circulation but substantial enough to maintain a distance between the knees perhaps equal to the width of the hips. Please note that hip bursitis often is complicated by a component of hip tendonitis which may also be alleviated with the advice of this article. Please also note that this is not the panacea of care for hip bursitis. Functional care involving nutrition, stretching, strengthening and physical medicine are advisable but beyond the scope of this article.