5 mysterious sleep-related conditions that researchers are still trying to figure out

The now-deceased PBS icon Bob Ross occupies a prominent if confusing space in the psyche of a small-but-growing chunk of the population. It's not Ross's artistic prowess that has posthumously earned him a following. Rather, it's the entrancing sounds of his brushstrokes and signature style of whisper-narrating his painting process. The calming, visceral effects of watching (or listening to) Ross create banal landscapes is a "condition" (for lack of a better term) that went unnamed until 2010. Then, thanks to online forums, the way Ross makes some people feel became known as ASMR, short for Autonomous Sensory Meridian Response.

The gist of ASMR is as puzzling as it is simple: For an unknown percentage of us, certain soft, repetitive or "close" sounds trigger physical tingles, as well as feelings of euphoria and relaxation. This might sound deserving of a fetish label, but the ASMR community doesn't consider the sensations erotic. Instead, the experience is often described as similar to a post-meditation calm. (Full disclosure: I unknowingly have had ASMR my whole life, and only stumbled on the term this past year; Bob Ross is my god.)

What's also curious about ASMR is that it's apparently common, and has potentially existed since the dawn of humankind, yet largely evaded formal scientific scrutiny. Since its 2010 "discovery," ASMR been the subject of only one peer-reviewed study, in 2014. And we don't really know what causes ASRM or why some people have it. Of course, ASMR is far from the only neurological whodunit related to sleep. To the contrary, the human nervous system is capable of all sorts of hijinks, some eye-opening, some laughable, some excruciating. Here are a few standouts that continue to challenge researchers.

More informally known as "Sleeping Beauty Syndrome," Klein-Levin Syndrome is a condition in which sufferers, typically adolescents, suddenly require extended periods of sleep — up to 23 hours a day for days, weeks or even months at a stretch. They may wake up only to eat or use the toilet, then collapse again due to unrelenting exhaustion. This need for sleep often comes with neurological symptoms, including weird food cravings, altered personality and a sudden lack of sexual inhibition. KLS was first named in 1962 but researchers have traced reports of the condition back to the early 1800s. There are theories about its cause — genetic factors may lie at the root — but still no reliable medical explanation. Luckily, KLS is exceedingly rare — with only one case per million people in the US.

Quite likely the greatest-named syndrome in the world, Exploding Head Syndrome (EHS) shouldn't be mistaken for the plot of "Scanners," as it's a largely benign sleep disorder. Sufferers describe being jolted awake by some variety of loud noise right as they're falling asleep or, in some cases, waking up. Think: gun shots, cymbal crash, explosions. Understandably, EHS is distressful to sufferers, for whom symptoms typically start around age 50. Researchers have yet to pin down a cause. Some believe EHS incidents are minor seizures. Others believe they're mechanical glitches caused by the inner ear. And many attribute EHS to psychological triggers, such as anxiety or stress.

Ask any parent what they fear most, and they will all say SIDS, the tragic boogeyman that continues to claim newborns while they sleep, for no known reason. People have known about the condition has been know about for centuries — some claim the Bible mentions it — but it only earned its acronym in 1963. Since then researchers have doubled down on studying SIDS. In the US, the number of cases has fallen by two-thirds since 1990, simply from counseling new parents to place sleeping babies on their backs. Despite such successes, researchers have yet to pin down the actual cause of SIDS, and it continues to be among nature's cruelest rituals, with some 3,500 SIDS deaths occurring per year in the U.S. alone.

The concept of Random Eye Movement underlies a phenomenon many of us have casually observed while watching other people sleep (yeah, we're all creeps): the quick, darting eyeball movements that happen while we dream. It's less well-known, however, that during REM sleep, your brain doses out chemicals that temporarily paralyze your muscles so you don't act out the light-saber fights and gymnastics of your nocturnal fantasies. For RBD sufferers, this little mechanism doesn't work so well, for unknown reasons, and the results range from the annoying, like sleep-kicking, to the hilarious, like sleepwalking naked down the street, to the dangerous-but-hilarious, like sleepwalking to the local Sleven, then hopping on a bus to visit an uncle the next town over. Researchers have isolated a few of the neurotransmitters responsible for the paralysis, but not the root cause, leaving RBD sufferers as the inevitable punch line of every pub night bullshit session.