The main purpose of sleeping is to restore brain chemicals — we all have biological internal clocks that alert us when the body and brain need rest (these times are usually 12AM-6AM and 1PM-3PM) and while asleep, your body produces new proteins and rejuvenates all of your internal systems.
When you’re sleeping, your brain releases the following chemicals: serotonin (which affects mood, emotion, and appetite), norepinephrine (which regulates stress response, heart rate, blood pressure, breathing, and your metabolism), and adenosine (the chemical compound naturally found in our body that causes drowsiness — caffeine actually blocks adenosine from properly binding and releasing energy, which is why caffeine keeps you awake).
So, when you’re sleep deprived and/or having trouble getting a good night’s sleep, the brain begins to malfunction because it can’t properly release these chemicals and do its job.
What’s happens first is the brain will begin turning off areas that aren’t absolutely necessary for survival. Consistent lack of sleep chips away at the strength of the prefrontal cortex in the brain — an area that supports logical and practical reasoning, as well as memory. Your prefrontal cortex has to exert a lot more energy than it should to do to make decisions and form memories — although it’s very, very likely you’ll experience insane difficulties recalling short-term memories (if at all), if you’re sleep deprived.
The next thing to happen is the body’s hormone levels go crazy. Your body will start overcompensating because it hasn’t properly been rested, and will start overproducing cortisol (which is a stress hormone). Cortisol then starts breaking down in your skin, which contributes to wrinkles and under-eye bags. Extreme unbalanced hormones, as a result of lack of sleep, then contributes to an increase in activity on the hypothalamus-pituitary-adrenal axis part of your brain, which controls and regulates your immune system (you’ll get sicker easier), your digestion (grehlin, a hormone involved in sparking your appetite, becomes overproduced and makes you hungrier more often; and as grehlin increases, leptin, the hormone responsible for suppressing appetite, decreases — putting you at risk for obesity and significant weight gain), sex (your libido lowers significantly), mood, energy, and reactions to stress.
You’re also more likely to become depressed — as mentioned before, certain chemicals that are released in your brain while you’re sleeping (such as serotonin) contribute to a natural anti-depressive effect. Without the proper amount of sleep, these chemicals aren’t functional in your brain.
Carrying out tasks becomes almost impossible when sleep deprived, because your brain starts shutting down your ability to utilize your working memory and minimizes your attention span. You’ll start to miss words while speaking or skip sentences while reading. Your reactions to things will be delayed and slow — a popular cause of car crashes is inattentiveness caused by sleep deprivation.
Sleep deprivation also completely warps your perception of things. Those who don’t sleep enough begin to elicit inappropriate behavioral and emotional responses to things — a study done at Harvard concluded that a group of subjects who didn’t sleep for 36 hours completely misread neutral images to be positive, suggesting that sleep deprivation can contribute to a sense of grandiosity and heightened emotional reactions to even the most normal and average things.
Another huge concern is that the brain has neural plasticity — which means, over time, the brain can adapt to new situations. What this means for people with consistently poor sleeping habits is that there is a threat that the brain can become severely damaged in the long-run and begin to be accustomed to not producing the chemicals and functionality you need.
Randy Gardner is one of the record holders for the longest time a human has (intentionally) stayed awake (without using any kind of stimulants). He completed the task when he was in high school in 1964, and lasted a full 264.4 hours — 11 days, 25 minutes.
The doctor who analyzed Gardner’s health after his experiment saw that Gardner was exhibiting serious cognitive and behavioral changes, all due to severe sleep deprivation. He began to show signs of trouble concentrating, recalling short term memories, and controlling his temper. He also was experiencing bouts of paranoia and hallucinations — all things he had never had to deal with prior to staying up for the 11 days.
Even though he was a good student in high school, the doctor recalls how on the last day of the experiment, he had asked Gardner to subtract seven repeatedly starting from 100. Gardner stopped at 65. When he was asked why he had stopped counting, Gardner said he had forgotten what he was doing. After staying awake for the full 264.4 hours, Gardner slept for only 14 hours, before naturally waking up again.
Sleep deprivation can have an incredibly debilitating effect on you physically, emotionally, and cognitively for the long-run. After Gardner and several other people tried to compete for holding the record for the longest time awake, Guinness World Records decided to stop recognizing sleep deprivation as a record holding category, because of the serious health risks it poses.