The optic nerve in your eyes senses the morning light. Then the SCN triggers the release of cortisol and other hormones to help you wake up. But when darkness comes at night, the SCN sends messages to the pineal gland. This gland triggers the release of the chemical melatonin.
We all have a built-in body clock, otherwise known as our circadian rhythm. This rhythm regulates the different functions of the body including your heart rate, hormone release, and body temperature. All these factors allow the body to wake up naturally and fall asleep at the right time within one 24-hour cycle.
A typical circadian rhythm in humans is one where peak alertness is around 2-3 hours after awakening and 9-10 hours after awakening, and where fatigue is most likely at around 3 AM, if you wake up like most people do at around 7-9 AM in the morning.
“There is no such thing as a “fixed or ideal time” to go to bed which will suit all individuals. It is generally advisable to fall asleep between 10 pm to midnight as for most people this is when the circadian rhythm is at a point that favours falling asleep.”
About an hour before you're supposed to wake up, PER levels rise (along with your body temperature and blood pressure). To prepare for the stress of waking, your body releases a cocktail of stress hormones, like cortisol. Gradually, your sleep becomes lighter and lighter. And that's why you wake up before your alarm.
Sleep inertia, or wake-up grogginess, is the main reason you're unable to fully wake up in the morning or after a nap. It's a completely normal part of your sleep-wake cycle that's intensified by factors like high sleep debt and circadian misalignment (caused by sleeping in, social jetlag, and travel jet lag).
When your body is well rested and you wake up on your own, it's a totally different feeling. If you wake up on your own before your alarm clock, and don't feel terrible, it's likely that you actually got enough sleep the night before.
"The overall best is if you can wake up naturally because you're done sleeping," he said. On the other hand, if you're waking up early on just a few hours of sleep, you should probably try and squeeze in some more shuteye.
If you aren't feeling rested when you wake up, despite getting to sleep at least 8 hours prior, then it might not be the quantity of your sleep that's the problem. It could be your sleep quality that needs some attention. The amount of sleep you get is important, but equally important is the quality of that sleep.
Sleep paralysis is a feeling of being conscious but unable to move. It occurs when a person passes between stages of wakefulness and sleep. During these transitions, you may be unable to move or speak for a few seconds up to a few minutes. Some people may also feel pressure or a sense of choking.
A person with an 8-hour sleep need who gets 6 hours each day for 5 days builds a sleep debt of 10 hours. As sleep debt builds, brain and body functioning deteriorate. Sleep is needed to “pay down” this debt.
Sleep paralysis happens when you cannot move your muscles as you are waking up or falling asleep. This is because you are in sleep mode but your brain is active. It's not clear why sleep paralysis can happen but it has been linked with: insomnia.
Why am I still tired after 8 hours of sleep? Most likely, you're still tired after 8 hours of sleep because you don't know your sleep need, you're getting less sleep than you think, you've got sleep debt, or you're out of sync with your circadian rhythm.
There could be a variety of reasons why you are still tired after sleeping for 8 hours. It could be due to poor sleep quality, lifestyle factors such as stress, poor diet, and lack of exercise or an underlying health condition.
The two most likely reasons you're always so tired no matter how much sleep you get are you've got high sleep debt or you're not living in sync with your circadian rhythm. You may also feel sleepy if you're ill, pregnant, or you've got a medical condition like anemia or diabetes.
If you've ruled out those conditions and are still hitting the snooze button after 9 hours under the covers, it might be a clue that you have an underlying medical condition such as heart disease, diabetes or depression. If you're an oversleeper, Polotsky recommends checking in with your doctor.