I can give one concrete example of where it definitely is causal.
There was a short BBC documentary series about sleep a few years ago, and one of the episodes focused on a man who slept for ten hours a day and still felt drowsy and without energy. After going through a sleep clinic with all kinds of tests, the conclusion was that he should try to sleep only six hours.
The basic issue was that because he spent ten hours a day in bed, trying to catch up on what he thought was a lack of sleeping causing his tiredness, his body never got tired enough to enter deep sleep. Because he missed his deep sleep cycles, his sleep did not recover his energy properly. So this was a vicious cycle.
After a few weeks of forcing himself to wake up after six hours of sleep his problems were basically solved.
So the thing to remember is that duration of sleep tells you nothing about the quality of sleep.
EDIT: While we're here, I've had a lot of sleeping problems in the past, so here some other tips that I remember from this series, and from my sister who studied chronobiology (the science of internal clocks in biological systems, including sleep cycles):
- Note emphasized enough by this article: the deep sleep cycle is necessary for cleaning your brain from neurodegenerating toxins[0]. Getting that stage three deep sleep is essential for your mental health!
- Don't use alcohol to induce sleepiness: yes, it makes you fall asleep faster, but it also prevents you from the deep sleep. You end up not being refreshed afterwards.
- Train your brain to associate your bed with sleeping. If you can't sleep, leave the bed, do something that's not so stimulating that it keeps you awake like reading a book (avoid that mobile phone at all cost) until you feel sleepy enough to go back. This article singles out teenagers here, which is ridiculous: adults are just as guilty of doing this to themselves.
- Because of the previous point, make sure you don't use your laptop/phone in bed, nor have a TV in the bedroom.
- The reason warm baths can help with falling sleep: a fast drop from a high core temperature to a low temperature triggers drowsiness. So what the bath does is heath you up until you are warm. If you then leave that bath and enter a cold bed that needs to be warmed up this triggers a sleep response. Hot milk probably gives a similar trigger, but I'm sure about that one.
- Fasting can help with jet lag. Specifically: don't eat for at least sixteen hours (drinking water is fine), then eat your first meal at breakfast (tangent: "break fast"). This resets the body clock.
This, so much. I went through a very similar experience - having tried spending longer and longer in bed in frustration at my insomnia, I did a course[1] that measured how much of that time I was actually asleep, then restricted my time in bed to that amount and no more. Having trained my body to sleep when in bed, I could then extend it slightly week by week, until I found the optimum I need (7.5 hours).
This is why it's common advice that if you cannot sleep, get out of bed. Go clean the house or do some light exercise until you feel tired, and then try again.
I can usually fall asleep fine, but will often wake up early and can't get back to sleep. If it's anytime after 5am, I just get up and start my day.
Fasting for jet lag: if you fast, then eat, digestion makes you tired. I read the exact same advice but with eating at dinner time of the destination. Doing so has helped me to get over jet large jet lag in a few days.
This is very interesting as the story sounds a lot like what I deal with. I have done the sleep apnea testing but that didn't show anything. It might be time to find a sleep clinic :)
Also good advice for improving quality of sleep, but it is a different kind of tiredness (or lack thereof).
The fact that there are multiple kinds of exhaustion, and that we might not distinguish them, can in itself be part of the problem, since you can end up trying to fix the wrong thing.
There was a short BBC documentary series about sleep a few years ago, and one of the episodes focused on a man who slept for ten hours a day and still felt drowsy and without energy. After going through a sleep clinic with all kinds of tests, the conclusion was that he should try to sleep only six hours.
The basic issue was that because he spent ten hours a day in bed, trying to catch up on what he thought was a lack of sleeping causing his tiredness, his body never got tired enough to enter deep sleep. Because he missed his deep sleep cycles, his sleep did not recover his energy properly. So this was a vicious cycle.
After a few weeks of forcing himself to wake up after six hours of sleep his problems were basically solved.
So the thing to remember is that duration of sleep tells you nothing about the quality of sleep.
EDIT: While we're here, I've had a lot of sleeping problems in the past, so here some other tips that I remember from this series, and from my sister who studied chronobiology (the science of internal clocks in biological systems, including sleep cycles):
- Note emphasized enough by this article: the deep sleep cycle is necessary for cleaning your brain from neurodegenerating toxins[0]. Getting that stage three deep sleep is essential for your mental health!
- Don't use alcohol to induce sleepiness: yes, it makes you fall asleep faster, but it also prevents you from the deep sleep. You end up not being refreshed afterwards.
- Train your brain to associate your bed with sleeping. If you can't sleep, leave the bed, do something that's not so stimulating that it keeps you awake like reading a book (avoid that mobile phone at all cost) until you feel sleepy enough to go back. This article singles out teenagers here, which is ridiculous: adults are just as guilty of doing this to themselves.
- Because of the previous point, make sure you don't use your laptop/phone in bed, nor have a TV in the bedroom.
- The reason warm baths can help with falling sleep: a fast drop from a high core temperature to a low temperature triggers drowsiness. So what the bath does is heath you up until you are warm. If you then leave that bath and enter a cold bed that needs to be warmed up this triggers a sleep response. Hot milk probably gives a similar trigger, but I'm sure about that one.
- Fasting can help with jet lag. Specifically: don't eat for at least sixteen hours (drinking water is fine), then eat your first meal at breakfast (tangent: "break fast"). This resets the body clock.
[0] https://www.nih.gov/news-events/news-releases/brain-may-flus...