why is is still hard to fall asleep when you’re sleep deprived?
In: Biology
To keep this as simple as possible for an ELI5, there are a number of things going on in your body that determine when you feel tired and when you actually fall asleep.
The two most important factors are your circadian rythym and sleep-wake homeostasis which are supposed to work in harmony to control your sleep cycle.
Circadian rythym is like a 24 hour internal clock controlled by your hypothalamus that affects a number of biological functions like your metabolism and hormone release, but most importantly when you feel alert and sleepy throughout the day.
Sleep-wake homeostasis is basically an internal measure of how much you need to sleep. This just continues to go up and up the longer you are awake.
It gets fairly complicated but both of these factors work together with a number of different areas of your brain when you are getting ready to sleep, making sure certain functions of your body stay active while others are switched off, e.g. the pons and medula signal muscles in your body to relax so that when you enter REM sleep and your thalamus is sending out visual and audio signals etc, you don’t start physically running in your bed because you are dreaming you are being chased down the street.
The problem is that because this process is so involved, so many different things can disrupt it, either by causing your circadian rythym and sleep-wake homeostasis to become out of-sync or getting in the way of the biological functions that allow the brain to work in the way we discussed to send you to sleep (release of chemicals melatonin and GABA etc).
Things like exposure to light, medicines or other chemicals you have ingested, medical conditions, the environment you’re trying to sleep in, your diet, how much physical activity you’ve done and stress can all greatly disrupt these functions. So ironically, if you’re super sleep deprived and feeling really tired, you might get anxious about whether you’re going to get enough sleep, especially if you have a big/important day coming up. That anxiety and worry could disrupt your ability to sleep even while you lie there feeling more exhausted than you’ve been all year.
It is related to the functions discussed above but there are also electrical patterns of brain activity that play a role in this. This starts to get quite complicated again and I’m already explaining it badly so I’ll just give a quick example. The reason why many people find it easy to fall asleep watching tv is because watching tv often only stimulates a very specific and small part of your brain. As the rest of the brain isn’t being actively used for anything, the electrical activity throughout the brain starts to die down, triggering the functions that get you ready for/send you to sleep. In the end the overwhelming desire of the rest of the brain to sleep also shuts down the part of your brain being stimulated by watching tv.
TLDR; the human body in general, and specifically sleep function, is very complicated and it is hard to give a short answer about what makes us sleepy and how we actually physically get to sleep. The best thing you can do is research the factors that are proven to affect sleep (exposure to light, sleep environment, stress, diet, level of physical activity, etc) and try to control them to the best of your ability. In the end, if you consistently struggle with sleep issues see a doctor as getting sufficient sleep is one of the most utterly important factors in good physical and mental health. The benefits of sleep have been demonstrated over and over and there are also many demonstrated serious negative effects from lack of sleep.
On that note, good night and sweet dreams!
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