During our waking hours, if our limbs feel uncomfortable we move our bodies until we feel more comfortable.This continual movement helps blood flow and helps to keep muscles relaxed. During sleep hours we move about much less and therefor are more prone to muscular problems.Try to avoid heavy duvets/blankets on the bed which may restrict movement especially around the area of the feet as this can cause unusual and uncomfortable twisting of the upper leg. Also bear in mind lower back problems may be part of the cause.