“You know, I’m not a big sleeper,” Donald Trump said last November. “I like three hours, four hours, I toss, I turn, I beep-de-beep, I want to find out what’s going on.”

It’s a classic set-up for sleep deprivation, and an article by Timothy Egan in the New York Times last February suggested explicitly that this might explain Trump’s erratic, irrational-seeming behavior such as lashing out at allies or potential allies, lack of remorse and grandiose thinking.

So now, during morning Neurology rounds, my colleagues and I often joke about whether patients of a particular temperament are suffering from what we called “Trump Syndrome”—a ravenous late-night craving for stimulation that results in a sometimes sporadic, often slender sleep schedule.

We certainly know what it feels like. Residency gives you an immersion course in Trump Syndrome, where strange things happen, especially when switching from day to night shift.

At the beginning of my two-week block of nights, I once sat down to document a patient’s history and physical exam, only to realize I hadn’t done the physical exam. Strange.

After urgently running down three flights of stairs and galumphing into the intensive care unit, I couldn’t remember why I had gone there. Huh.

Did I really space out long enough for my screen saver to come on? Bizarre.

Such moments had a tingling, stretched-out texture, as if time had somehow pulled apart my train of thought like salt water taffy.

Towards the end of my second week, I Googled “sleep deprivation” and discovered that neuroscientists deprive healthy people of sleep as a surrogate model of psychosis. And that’s when I first discovered Timothy Egan’s piece. It all started to come together.

Sleep deprivation is an area of intensive research. For millions of years, our brains evolved to work during the day, sleep at night. In most parts of the world, daylight lasts about 15 hours (depending on where you live), so there was no reason to have a brain that lasted much longer. That is, until the light bulb was invented.

Charles Czeisler of Harvard Medical School credits electric lighting fueled by cheap energy for sleep depriving much of our world. “Technology,” he wrote, “has effectively decoupled us from the natural 24-hour day to which our bodies evolved, driving us to go to bed later. And we use caffeine in the morning to rise as early as we ever did, putting the squeeze on sleep.”

I am, in fact, writing this long after sunset and know I will need at least a double espresso to squeeze through morning rounds.

The U.S. Center for Disease Control (CDC) reports that, in a survey of nearly 75,000 people, 35% of respondents reported less than seven hours of sleep per night with nearly 30% reporting less than six. A startling 38% of adults reported unintentionally falling asleep during the day.

It appears the screen saver phenomenon is endemic, hopefully less so in leaders of the free world.

Sleep deprivation rapidly restructures brain function. Neuroscientists at the Universities of Oslo and Oxford used functional MRI to study how the brain changes with sleep deprivation. They scanned sixty people in the morning, evening, and following morning after some had slept a full night and some had not slept at all.

The difference in brain function was startling and involved nearly every neural system. So stark that—based on brain function alone—a machine learning algorithm identified sleep deprived from well-rested participants with 90% accuracy. In the machine-learning world, 90% accuracy is YUGE! A big, big, large, very large signal.

Brain regions associated with judgment, memory, and emotion are the most strongly affected by sleep deprivation. It’s as if sleep deprivation slows our cognitive machine to a grind and—as the researchers showed—sleep allows brain networks to reset to their healthy rhythms.

It’s easy to cite studies that sleep deprivation deteriorates memory consolidation, reaction time, the ability to think creatively, and even recognize another’s emotions.

Sleep deprivation also has subtle effects, like shifting our economic preference from defending against losses to seeking increased gain; shifting the art of any deal towards aggression, away from balanced thought.

So the next time you consider sending that late-night Tweet or (hopefully not) work-related email, don’t succumb to “Trump Syndrome.” Remember: being awake longer than about 15.8 hours comes at a cost, even if you don’t feel sleepy.