Fatal Familial Insomnia

Yes, this is another syndrome that was featured on "20/20," but it's a fascinating illness (and thankfully rare), so I thought readers might want to know more about it. You can find an article from ABC that pretty much sums up the "20/20" feature here.

For a more scientific explanation, you can read an article from the University of Michigan. As it explains, the disease is caused by degeneration of a certain region of the mind, the thalamus. As the article notes, "Sleep, blood pressure, heart rate, body core temperature and hormone flow are all affected by the interruption of the body's circadian rhythms which is a direct result of the degeneration of the thalamus in this disease."

Symptoms of Fatal Familial Insomnia can include an inability to feel pain and poor reflexes, and the lack of sleep can cause the sufferer to experience hallucinations and eventually fall into a coma.