Restless Leg Syndrome
Known as the most common disease nobody knows about, Restless Leg Syndrome (RLS) effects 6-9% of the population, to varying degrees. Typically producing a deep feeling of leg discomfort at night, relieved by motion, when it is severe RLS can interfere with sleep and cause daytime drowsiness. It also can cause significant discomfort, approaching pain, on long flights and train trips when movement is restricted. No-one dies from it, but it can be a real annoyance, and it is often mis-diagnosed or dismissed.
I myself have a mild case of it, and it makes me nuts on airplanes, mainly. I cannot sleep on planes and like to stand up next to the bulkheads. For the many who are bothered by RLS, there are effective treatments now if it bothers you enough. Neurologists tend to be the ones who would be familiar with the new treatments for this poorly-understood ailment. The latest information is available on Medscape.com, which I cannot link right now.