What causes EHS?
EHS seems to be a sleep disorder that is becoming widely studied and acknowledged in the United States, but people living in other parts of the world, who are likely to be struggling with these symptoms, might not be aware of these recent findings. Brian Sharpless, an assistant professor and director of the psychology clinic at Washington State University and the lead researcher of the largest study on EHS, told CBS news that "the noise people hear in their heads stems from a momentary neural hiccup as the brain transitions into sleep mode."
CBS news reports that Sharpless compares it to a computer shutting down, with the brain's motor, auditory, and visual neurons turning off in stages. Once in a while, instead of shutting down properly, the auditory neurons fire all at once. "That's why you get these crazy-loud noises that you can't explain, and they're not actual noises in your environment," he said.