What happens when we sleep?
Most of us know that sleep is good for us, whether we get enough of it or not. But what actually happens to our body during this time? Here’s what we know:
The entire process occurs over four stages and, just to complicate matters, all of these stages happen in cycles — usually four or five per night. So sleep cycle apps attempt to estimate how many cycles you’ve been through in order to wake you up during the lightest phase of sleep.
A typical cycle starts with the non-rapid eye movement phase (NREM). There are three major stages of NREM before deep rest. The first one contributes to between five and 10 percent of an adult’s total sleep experience, where your brain is still conscious, though you slowly start to feel more relaxed. Try to watch someone nodding off. If they’re twitching and jerking, they’re in this stage. And incidentally, the more you think about trying to get to sleep, the longer you will remain in this zone.
Stage two, which makes up 45 to 55 percent of the total, is where you move completely into sleep paralysis. Muscular movement decreases, and your conscious awareness of the external environment disappears. Dreaming is still very rare, however, and you can easily be awakened. In fact, some scientists estimate that the average person wakes up between five and 15 times every hour when shifting from one stage of sleep to the next. You simply don’t notice it because it happens so quickly.
Next up is stage three, also known as slow-wave sleep, contributing to between 15 and 25 percent of your total. This is where you become far less responsive to the surrounding environment and your body no longer produces any reactions. This deep sleep is considered to be the most restful, but it’s not all roses and rainbows: this is also where things such as night terrors, sleepwalking, and somniloquy (sleep-talking) occur. So if you’ve ever admitted your deepest, darkest secrets out loud in the middle of the night, blame stage three of the NREM cycle.
The most fascinating thing of all about sleep? Just how little we actually know about what goes on when we’re resting
The fourth and final stage is known as REM (rapid-eye-movement sleep) and it takes approximately an hour-and-a-half for your brain to get into this phase. This is where most of your dreams will occur, despite only making up a miniscule proportion of your sleep. It’s also the point where things go a little haywire, as your eyes begin to rapidly move behind your eyelids, hence the name. Most of your muscles become paralysed, but your heart rate, breathing and body temperature all become less regulated. Brain waves can rise to levels equivalent to those of waking, allowing your most vivid dreams to be projected.
Studies have shown the body restores itself most efficiently during REM, hence proper rest is so important to aspects such as muscular growth and recovery following exercise. Sleep causes the secretion of HGH, a hormone that promotes the growth, maintenance and repair of muscles and bones.
The flipside is that sleep deprivation negatively affects the immune system, as the body’s level of disease-fighting agents rises significantly during sleep and drop substantially when awake. The production of white blood cells, which are necessary in forming our body’s defence system, also increase during sleep.
The recommended amount of sleep is somewhere between seven and nine hours, but it hasn’t always been this way. Some nomadic societies exhibit far more disjointed routines, sleeping at all times of the day and night for shorter periods, depending on the habits of the animals they’re hunting.
Patterns have also changed significantly since the introduction of artificial light in the mid-1800s, due to our body’s circadian clock being profoundly sensitive to changes in light. People without access to artificial light often go to sleep far sooner after the sun has set, so it’s no wonder that the sleeping patterns of pre-industrial times are vastly different to those seen today. In fact, evidence suggests we used to spread out our night’s sleep over two shorter periods, beginning the night with a period of sleep of four hours or so, following it with a state of wakefulness for the next three, and then sleeping through until morning.
But the most fascinating thing of all about sleep is just how little we really know about it. To this day we’ve failed to work out the purpose of dreaming, despite hypotheses from great minds like Sigmund Freud’s. And maybe it’s okay that our dreams remain elusive and just out of reach.