Editor's Note: The following contains spoilers for the Netflix series, The Sandman.

What would happen if a warlock managed to capture an entity that represents one of the core aspects of our existence? Say, for instance, our ability to dream. The first episode of Netflix’s new series, The Sandman, offers a fantastical answer to that even more outlandish question. Based on the first volume of Neil Gaiman’s Sandman comics, “Sleep of the Just” has the occultist leader Roderick Burgess (Charles Dance) capturing Morpheus (Tom Sturridge), the Lord of Dreams himself. The third born Endless is trapped for decades in an egg-like glass cage, uselessly blackmailed with promises of release in exchange for bringing Burgess’ son back to life.

During Morpheus' captivity, dreams and nightmares alike are left free to roam the Earth, and people all over the world find themselves afflicted by a strange illness. As Dream himself explains, some beg for sleep that will not come, while others live as perpetual sleepwalkers. And then there are those that fall asleep never to wake again. All of this sounds delightfully terrifying and impossible, as is expected from a show in which intangible aspects of life, such as Death, Dream, and Desire take human form. However, the sleeping sickness that appears in The Sandman was based on a very real disease that took the world by storm in the 1910s and 1920s — and whose cause remains a mystery to this day.

Nowadays, when people say sleeping sickness, they are usually referring to an infection caused by bug-carried protozoans found in parts of Africa. However, despite being potentially fatal, the African trypanosomiasis doesn’t cause any kind of deep slumber, though the symptoms may include alterations in the sleep cycle, according to the World Health Organization. The disease that was first described by Dr. Constantin von Economo in 1917, and that eventually made its way into Neil Gaiman’s body of work, was much more directly connected to the patients’ level of alertness. The encephalitis lethargica, as the disease came to be known, threw its victims into a deep sleep-like, motionless state. Some were virtually transformed into living, breathing statues while in the middle of regular activities, such as working or eating lunch.

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Image via Netflix

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The disease’s name and the period in which it was first described match the events of “Sleep of the Just.” In The Sandman’s first episode, we learn, from Sturridge’s deep voice, that a disease doctors named encephalitis lethargica took over a world that would soon be at war again — a reference to World Wars I (1914-1918) and II (1939-1945). On-screen, we see a hospital filled with sleep-deprived and sleep-stricken patients in 1926, in the middle of an epidemic that affected over a million people across continents, leading to more than 500,000 deaths up until 1930. But what exactly happened with these people? And what caused them to fall ill?

The precise cause of the encephalitis lethargica is still a mystery. At the time of the epidemic, some speculated that it might have something to do with the influenza pandemic of 1918, more commonly known as the Spanish flu. After all, the sudden rise in cases of encephalitis lethargica happened about the same time as the world was recovering from the flu. Still, there was no other evidence suggesting that the two diseases were connected. Ties between the sleeping sickness and polio were also theorized, as well as the possibility of the illness being the result of an autoimmune condition.

The Sandman-sleeping sickness

Some doctors and researchers have come up with theories attributing the illness to bacterial or viral infections. In 2004, a study suggested that rare bacteria of the streptococcus kind could be behind the disease, but, according to a paper published in Brain, a journal of neurology,, the researchers involved in the project have since moved away from the hypothesis. In the same paper, penned by Dr. Joel A. Vilensky and Dr. Leslie A. Hoffman, there is mention of a 2012 study connecting both old and more recent cases of the illness to an enterovirus. However, due to the scarcity and the poor quality of existing brain tissues from the epidemic, as well as to the rarity of new cases, replicating such a study proved to be too hard, and the enterovirus theory remained just a theory.

Research on the causes of the encephalitis lethargica epidemic slowed down as new cases became rarer, around the late 1920s. Just a little before that, millions went to their doctors with complaints of fever, delirium, involuntary movements, headaches, and muscle rigidity, among other things. In the most severe of cases, they fell into a strange, decades-long coma. Those affected by the gravest form of the illness, named somnolent-ophthalmoplegic by Dr. von Economo, had a 50% chance of dying from inflammation of the brain, internal hemorrhage, and respiratory failure.

But even those that managed to escape the deep, endless slumber still faced tremendous risk. Years would go by until seemingly cured patients presented signs of the chronic form of the disease. The symptoms included involuntary movement of the eyes, psychiatric disorders that could go from euphoria to psychosis, and, perhaps most prominently, a great stiffness of the upper body denominated post-encephalitic parkinsonism. With time, patients would stop moving entirely, their bodies still and their faces frozen in a kind of mask. Most would be committed to hospitals where they would spend the rest of their lives under care.

Oddly enough, though, the paralysis caused by the chronic form of the sleeping sickness could be circumvented by things such as throwing a ball to the afflicted person or putting on some music. The external stimulus would cause the sick to lift their arms to catch the ball or even dance for a while. This kind of response to the outside world led neurologist Oliver Sacks to believe that there was something more to the disease than what was known at the time. Sacks, who would eventually become a renowned author, was a doctor at the Mount Carmel Hospital in New York back in 1969. Working in a ward that housed about 80 patients with encephalitis lethargica, he decided to try a new drug that had positive results in treating Parkinson’s disease: levodopa.

The results of Dr. Sacks’ experiments were immediate and nothing short of miraculous. Patients that had spent nearly 50 years bound to beds and wheelchairs, incapable of moving a single muscle, could suddenly walk and talk like they had just woken up from a nap. Everyone was ecstatic, and, for a while, it seemed like Dr. Sacks had found a cure for a disease that had puzzled the medical community for decades. Alas, the joy was short-lived: though levodopa had its effects on the patients’ brains, it could not mend the neuroconnections damaged by the disease. With time, those that had woken up began suffering from tremors, psychosis, violent mood swings, and many other symptoms were also present in earlier cases of chronic encephalitis lethargica. The treatment was interrupted, and the awoken returned to their catatonic state.

Sandman

Still, their brief return to the waking world was essential to our better understanding of the human mind. The success and subsequent failure of levodopa in treating encephalitis lethargica enlightened doctors and researchers about the role dopamine plays in different parts of the brain. And, while they were awake, Sacks’ patients were able to tell him about what it was like to spend all that time trapped behind their own skin. Though some did behave like they had just come out of a coma, completely unaware of the passage of time, others revealed that they had been 100% conscious throughout all those years.

Dr. Sacks recounted his experience at Mount Carmel in the 1973 book Awakenings. One of the stories he tells is of a patient identified as Rose R., who went to bed one night as a 21-year-old, in 1926, and was only able to get up after 43 years. Rose could recall details of events that took place after she was already in a catatonic state, such as the attack on Pearl Harbor, and claimed to have had a dream in which she was turned into a statue of stone on her last night as a carefree young woman.

Awakenings was adapted into a movie of the same name in 1990. Directed by Penny Marshall, the film stars Robin Williams as Dr. Malcolm Sayer, a fictionalized version of Dr. Sacks. Robert De Niro stars opposite Williams as patient Leonard Lowe, who contracted encephalitis lethargica as a young boy and is only able to communicate with Dr. Sayer through a Ouija board — that is, until the titular awakening.

The real Leonard passed away in 1981. Rose R. died in 1979, having choked on her dinner. After Dr. Sacks’ short-lived medical miracle, there were no other documented “awakenings.” Thankfully, though, the number of cases of encephalitis lethargica has also dropped considerably after the epidemic of the 1920s. According to Dr. Vilensky and Hoffman, from 1941 to 2009, there were little more than 200 documented new occurrences of the disease, and it’s impossible to tell for sure whether the new patients have the same syndrome as the ones that fell ill during the epidemic. In great part, the sleeping sickness seems to have been contained to a mere decade-and-a-half in the early 20th century.

Overall, the encephalitis lethargica epidemic remains one of the greatest mysteries of contemporary medicine. Alongside its cause, it is still unknown why the disease died down so suddenly and why so many cases emerged all at once. Perhaps most importantly, it is unknown whether an epidemic like this could happen again. In order to avoid ending this article on such a down note, I suggest we look at the world of fantasy for a little solace: as long as no one tries to capture the Lord of Dreams again, we shall be safe.