When it comes to diseases of civilization, low back pain is public enemy number one. Often this condition is caused by tight hip flexors, which can manifest as low back pain or the sensation that one's hips are tied in knots. If you experience hip tightness during the night, specifically, this is good news. It reduces the possible causes and simplifies treatment.
Night Time Causes
Poor posture while sleeping can cause hip tightness. It can result from any favored sleeping position -- back, side or belly. It could be caused by an old mattress or failing to stretch after exercising in the afternoon. In the case of the latter, the muscles will have failed to relax, causing the hip flexors to tug on the low back when lying on your side or prone.
Change Your Sleep Habits
If you sleep on your back, place a pillow under your knees. If sleeping on your side, place the pillow between your knees. Although some people find relief from sleeping on their belly, if the position causes pain adopt one of the recommended modifications.
When dealing with hip dysfunction, it's best to cover all your bases and this includes stretching regularly. Perform a kneeling hip-flexor stretch. In a genuflecting position, keep the front leg at a right angle as you drive your rear leg backward. Keep your core tight and your torso upright. Since other muscles may be silent accomplices to hip tightness, add in a simple hamstring stretch. Sit down with your legs extended forward. Bend at the waist, reaching for your toes. Maintain a straight back. Do not hunch over. Accumulate 30 to 90 seconds per stretch.