Imagine getting sick and then slipping into a sleep you can’t wake up from, not for days, not for months, sometimes not for years. In the early 1900s, a mysterious “sleeping sickness” known as encephalitis lethargica swept across the world, leaving people frozen between life and death: eyes closed, bodies still, but often aware of everything happening around them.

Doctors watched as some patients never woke up, while others opened their eyes decades later with strange, permanent damage to their brains, turning one baffling illness into one of medicine’s most haunting unsolved stories.