Fairy tales made their way into the modern literacy sphere when French author Charles Perrault, in 1697, published Histoires ou contes du temps passé (literally, “Stories or tales of times past”). Histoires was a collection of stories which quickly permeated our culture, including the now-famous Cinderella, Puss in Boots, Little Red Riding Hood, and Sleeping Beauty. Whatever basis Perrault’s stories have in reality are, at best, quite tenuous — one doesn’t see pumpkins-as-chariots, swashbuckling cats, or wolves wearing grandma’s bed clothes in the real world.

The sleeping for a century part of the Sleeping Beauty tale is, also, total fiction. But sleeping for days on end is amazingly not. It is perfectly possible and, if it happens, most likely due to a neurological disorder called Kleine-Levin Syndrome (KLS), or, colloquially, Sleeping Beauty Syndrome.

Those affected by KLS sleep the whole day and night away, waking only to eat and use the bathroom, and typically only briefly at that (although some KLS sufferers report elongated eating binges). While awake, the person appears zombie-like, having little energy and showing even less emotion. Many are unable to even communicate while awake. In extreme cases, such as the case of Louise Ball in the UK, episodes can last as long as ten days and waking up is rare. Caretakers (in Ball’s case, her parents) are instructed to try and wake the person to get him or her to use the bathroom and try to eat.

KLS is most prevalent in teenagers (lending itself to an easy joke about lazy teens who like to sleep all day, a trait The Onion recently mocked), with the first onset occurring, on average, at about age 15 — and with no discernible cause. Episodes can occur as frequently as every few weeks to only once in five years, but on average, the sleeping spells occur every six months. By a KLS sufferer’s mid to late 20s, the syndrome often disappears, again with no discernible cause. Similarly, KLS is incredibly difficult to diagnose, as there are no markers unique to it other than the symptom set, and physicians need to eliminate all other possible causes before declaring KLS the cause of the lethargy. Because of this, the syndrome often takes years to correctly diagnose.

The good news is that it is extremely rare: It affects only about six people in ten thousand.

Bonus fact : Another sleep-related disorder is called “Non-24-hour sleep wake disorder.” People affected by Non-24 have internal body clocks which refuse to acknowledge the standard 24 hour cycle of a day and therefore do not necessarily associate night with sleep and day with being awake. (For example, a person whose natural internal body clock was 28 hours long would seek sleep at intervals four hours later each day, incrementally, than typical people would.) Most interestingly, while Non-24 affects both blind people and sighted ones, it is very prevalent in blind people who do lack light sensitivity, suggesting that our body clocks are a function of the Earth’s rotation.

From the Archives: Allergic to Paris: Another odd and rare syndrome, although not involving sleep.

Related: A totally inappropriate book for anyone suffering from KLS (and probably Non-24, too).