Dr. Ellen Vora, a psychiatrist specializing in sleep disorders, was the guest on a podcast I heard recently, during which she explained that overtired is not equivalent to exhausted or wicked tired. It’s a thing unto itself.

When you are tired, you may find yourself dozing off unexpectedly. Your eyes droop, and you don’t feel like doing much. If this happens in the evening as the sun is falling, it’s a perfectly healthy reaction. As our day winds down, and light changes from blue to red, our bodies prepare for sleep, producing melatonin. For most of our existence, when we got tired, we slept.

Even on the savanna, though, there are times when you have to stay awake. Maybe you’re giving birth, or helping someone else do so. Maybe it’s your night to guard the tribe from a man-eating tiger lurking about. Maybe you’re a soldier preparing for a night battle. In those cases, you will have to fight the urge to sleep, and your body is happy to help. As you raise your activity level, or expose yourself to brighter light, preparation for sleep is not only halted but reversed, and your body prepares instead for action.

That is, our bodies evolved not only to help us sleep at night, but also to support us when we choose not to.

Since the invention of electricity, we have chosen to stay awake a lot more often than we bear children or fight predators or enemies. The condition of tiredness that we reach after reversing our natural pre-sleep chemistry then staying up for a while is characterized by exhaustion combined with inability to fall asleep, sometimes for the rest of the night, ie, being overtired, and as a regular occurrence, it’s not very good for us.

As well as being a sleep doctor, Dr. Vora is a married woman with a 4-year-old so her house goes “full Game of Thrones” at sunset. It’s not the violence or sex she’s talking about, but rather the presence of electric lights and light-producing screens. That is, there are none.  Her family lives by candlelight–or maybe torchlight, which seems more GOT. She likens their bedrooms to caves, with room-darkening shades that prevent one from seeing one’s own hand in front of one’s face.

She practices in NYC, and notably saw a day’s worth of patients after a blackout, each of whom was both overjoyed by their sleep quality the previous night and disgruntled about the boredom and inconvenience of the blackout. Sometimes we humans miss the obvious.