Sleep, on a personal level, is incredibly frustrating. Wasting around seven to eight hours of every single day of our adult life on it seems like a colossal waste of time to me when there’s so much fun to be had while conscious, but it’s difficult to deny the vital health benefits that regular, unbroken, proper sleep – as elusive as that is – brings about.

Sleep deprivation (SD), whether intentional or inadvertent, takes them away, and it’s indubitable that you’ll miss them the moment they’re gone. So let’s journey, step-by-step, through what you enjoy when you sufficiently snooze, and what the myriad effects of a total loss of sleep may be, with the caveat that some of these effects remain decidedly enigmatic.

As is well known, you go through various phases of sleep, which form part of multiple cycles. When you engage in rapid eye movement (REM) sleep, you dream, and perhaps sleep-walk or talk, but this only makes up a small portion of your presumably nocturnal activities.

For the majority (75 percent or so) of your snoozing, you enter non-rapid eye movement (NREM) sleep, which comes in three distinct phases. During N1, you fluctuate between being awake and asleep, and not too much happens to you on a physiological level – although some of you may experience hypnic jerks, sudden muscle spasms that may shake you awake.

When N2 occurs, sleep begins in earnest, and you become unaware of your surroundings. Breathing and heart rate remain regular, but your core body temperature drops. N3, however – colloquially referred to as “deep sleep” – is where all the good stuff tends to happen.

As your blood pressure drops and stays low – which boosts cardiovascular health – your muscles relax and your breathing slows, and the blood supply to your muscles increases. Tissue growth and repairs are prioritized, and hormones vital to your proper functioning are released, including those that regulate feelings of hunger.

 

Your hippocampus, which deals with memory consolidation – among other things – shows plenty of electrical activity as you slumber. Although much remains unclear, recent studies have suggested that short-term memories acquired throughout the day appear to be progressively transferred to the cortex for long-term “storage” at night.

Something that falls away immediately after just one less night of sleep is those all-important cognitive reasoning and retention functions. From grammatical reasoning and spatial planning to memory recall activities, our abilities begin to drop off to varying degrees.

It appears that there’s far less activity going on in the frontal and parietal lobes, which deal with problem-solving and decision making. As noted by a landmark 2017 review on the subject, your visual cortical regions also show an increasingly reduced signal over time during visual working memory tasks. Reaction times and learning also fall by the wayside.

The brain’s reward system is also shown to be sensitive to SD, which can cause changes in how a person seeks out risks, sensations, and takes impulsive actions. Essentially, the more SD you experience, the more of a clumsy fool you’re likely to become.

The 2017 review also notes that based on the “limited evidence to date”, SD begins to trigger reductions in the brain’s “intrinsic connectivity profile”, essentially meaning that the wiring linking up parts of your brain become less effective. A separate study highlights that brain cells themselves are less able to communicate with each other too. This is also one of the reasons why you become physically uncoordinated as SD worsens.

This, along with reduced blood flow to said regions, is thought to be connected to not just cognitive, but “emotional impairments”.

A piece on the phenomenon over at LiveScience explains that SD makes the person less able to display positive emotions, and less able to recognize them in other people. Negative emotional experiences become increasingly harder to deal with as the days go on, and some people may experience a state of delirium and even hallucinations.

Whether or not they’re true, full-blown hallucinations or merely ephemeral flickers in their peripheral vision are up for debate, but either way, the brain will be less able to process sensory information as times ticks by.

Physical health is inextricably linked with mental health, too. Those that sleep well are far less likely to experience depression, anxiety, and other related mental health problems. In the absence of it, such afflictions may appear or worsen if already present.

SD means that those feeling of famishment-controlling hormones aren’t being released in quite the same way either, and your body stops metabolizing glucose efficiently. As noted by Slate, you’re consequently going to desire more carbohydrates than necessary, which may indirectly lead to weight gain in the long run.

Even with a single sleepless day in tow, cortisol and thyroid-stimulating hormone levels rise, triggering a higher blood pressure. In the long term, poorer cardiovascular health probably awaits you.

Lest we forget the health of your immune system. A good night’s sleep allows your body to promote the production of cytokines, a family of proteins vital for communication between cells. Similarly, solid snore-sessions allow you to maintain normal levels of immune system cells and associated antibodies.

Over time, through SD, it’s likely your ability to fend off infections will begin to falter as its immune responses are suppressed.

Evidence in mice suggests that sleep may even “flush” toxins out of the brain. Experiments show that the space between our critter cousins’ brain cells increases during the unconscious night by up to 60 percent.

As this happens, cerebrospinal fluid floods through the valleys, clearing out toxic byproducts that are associated with neurological impairments as well as far more serious neurodegenerative disorders. In the long term, then, SD – or chronic sleep loss – could potentially increase a person’s risk of gaining said disorders later in life.

A day-by-day account of what happens to an individual is difficult to elucidate upon, as such experiments are difficult to maintain in the long run, and people respond differently to sleep loss. Is the end always the same though? Would a near-perpetual SD experience always end in death?

It’s possible, but there's not enough data to say one way or the other. The detrimental health effects would probably finish you off if you managed to keep going, but there’s almost no way in which this is possible as you’d increasingly struggle not to fall asleep no matter what you were doing to try to prevent that; your brain would forcefully begin to shut down. Anecdotal evidence of humans dying after 11 days, then, aren’t reliable data points.

Curiously, as described by The New York Times, in a set of SD experiments on rats, those totally deprived of sleep died in 2.5 weeks; those deprived of just REM sleep took twice as long to perish. Importantly, though, it’s not clear what the cause of death specifically was, just as it’s still not entirely clear why, in many aspects, sleep is so necessary for our continued survival.

In any case, you don’t need to undergo total SD to live through such a hellish life. From temporary disruption to insomnia, much of civilization is sleep deprived – and we’re sleepwalking into a health-based nightmare as a result.