A look at hypersomnolence, a condition that causes a person to sleep excessively, and the difficulty of treating a rare sleeping disorder:

Sumner needed sleep like an addict needs a fix. ‘It was this overpowering desire in me, a physical urge,’ she says. ‘And there was always the hope that, maybe this time, I would wake up feeling better.’

Sumner was almost 30 before finally confronting her problem. She had joined a high-profile law firm in Atlanta and, for the first time in her life, didn’t have a flexible schedule. She couldn’t nap without raising eyebrows. ‘That’s when it finally hit me,’ she says. ‘This is not how you’re supposed to feel.’

In the fall of 2005, she sought help at the Emory Clinic Sleep Center. She learned that her problem, known as hypersomnolence, was rare but not unheard of. Over the next six years, a team of doctors there analyzed the chemicals in her brain and in the brains of 31 other hypersomniacs. They fingered one mysterious substance as the culprit.

“Re-Awakenings.” — Virginia Hughes, The Last Word on Nothing