I just don’t understand, some days, usually on weekends, I’ll try and wake up after a normal amount of sleep (like 7.5-8 hours) but I feel too exhausted to wake up.
Then I’ll end up sleeping like 12 hours and I feel like crap all day. Why is this?
In: Biology
There are three major reasons for that:
1.) Your sleep cycle: The average person goes through four to six sleep cycles per night. Each one of those cycles is approximately 90 minutes long. To put it simply, there is light sleep, deep sleep and REM sleep (this is when you dream) in every sleep cycle and the longer you sleep the longer gets the REM part of your sleep cycle. This is also the reason you dream a lot (and a lot of nonsense) when you sleep longer than usually. Now, waking up from REM sleep, doesn’t feel that good and you are often very confused, especially after longer periods of REM sleep.
2.) Your biological clock (also known as the “circadian rhythm”: You have to understand that *each and* *every* cell in your body is a seperate clock. They all add up to your “circadian rhythm” – which is essentially your body controlling all of your metabolic system through the release of hormones and the accumulation of waste material (All of it together says your brain when to feel awake or tired). Whenever there is a disturbance of your biological clock (e.g. sleeping longer or shorter than usually or flying overseas -> Jetlag) it causes a mess in your endocrine system (hormone system) and you feel tired and dizzy. This is also *very* simplified but you can read up on chronobiology if you want to understand more.
3.) Your personal lifestyle, age and genetics: How much sleep you really need is strongly influenced by your age (older people need less, children and teenagers need more) and your genetics (There are indeed *chronotypes* – such as owls and larks/morning persons and evening persons; this is not only a saying but scientifically proven.) Whenever you sleep less or more than you need to according to your age and genetics it leads to point 2.).
Finally, if your working night shifts and if you don’t have fixed sleep habits it leads to a messed up sleep cycle (point 1) and your biological clock stops working properly.
*I’m a German medical student and we were very lucky to hear a lot about sleep science, because one of our profs is very dedicated to the field. You can grab any book on chronobiology to read up more on that. By the way, the discovery of the biological clock was awarded with the nobel prize only in the year 2017:
[https://www.nobelprize.org/prizes/medicine/2017/summary/](https://www.nobelprize.org/prizes/medicine/2017/summary/)
Here some additional literature on the topic:
[https://www.health.harvard.edu/blog/little-sleep-much-affect-memory-201405027136](https://www.health.harvard.edu/blog/little-sleep-much-affect-memory-201405027136)
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4165901/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4165901/)
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