You climb into bed, turn off the light, and close your eyes, but you can't fall asleep. For most of us, it's just one annoying night, but for people with fatal familial insomnia, or FFI, it's the beginning of the end. An extremely rare genetic disease passed down through generations, FFI's primary symptom is sleeplessness, but with a fatal twist: victims are dead within months. To understand FFI, National Geographic delves into the s
