It is likely that the firm edge of the bed contributed to their focal compression palsy. All had slept with a partner and developed weakness in the leg on the side of the bed that they normally slept on. It is possible that as a person rolls towards the middle of the bed and their body sinks, the near leg rides up and over the firm edge. Alternatively, if the legs are crossed on a waterbed, the weight of the top leg may push the near leg under and across into the submerged edge. Peroneal nerve palsy is usually caused by external compression, and may be seen after anaesthesia, intoxication, coma or prolonged bed rest.
Many case reports, however, give no clear history of compression.
The nerve palsy is often ascribed to abnormal sleep postures, as symptoms are usually first noticed on awakening. It is not clear how many of these patients may have slept on waterbeds. Waterbeds certainly have benefits in some circumstances but we have every reason to be apprehensive about the cutting edge of technology. Until we do, peroneal nerve palsy will continue to remain a matter of gravity. Arnott N. Elements of physics or natural philosophy, vol 1.