Okay so first of all, this is a long thread but please take your time reading this as it took me hours to write and edit; you won't regret it, I promise you.
So I have recently stumbled upon lots of people here who say "Even though I sleep 8-9 hours, I'm still tired." and a lot of others who just generally believe that more sleep = more energy + better well-being.
This is NOT TRUE.
When you go to sleep, your body enters different "stages" of sleep. There are 5 overall stages and together they count as 1 "cycle". During the night, these cycles keep repeating until you wake up. 1 cycle lasts approximately 90 minutes but it varies from person to person. You might think this is nonsense but keep reading, you will benefit greatly.
THE IMPORTANT THING: There are 2 ways in which you can wake up. Full of energy and positivity or completely tired with a bad mood. These 2 are NOT a result of either sleeping more or less; they are a result of you either waking up at the end of a particular cycle, or cancelling a cycle by being interrupted by an external source. Read below.
If you finish a cycle successfully and wake up, you will feel brilliant, full of energy and positivity. If your cycle is interrupted by an external source (you wanting to pee, parents/friends waking you up), you will feel terrible / grumpy and you will feel like you need "more sleep". Also, if in some mornings you wake up full of energy (which means you have just finished a cycle), and then force yourself to sleep more, there's a good chance you won't finish that newly entered cycle since you're just lazing about for 10 minutes and that will result in you waking up feeling tired again. And this is not just about waking up tired; this is about how your energy will be used throughout your entire day.
Side note 1: Sometimes you will find yourself lucky in a way that even though someone wakes you up which is an interruption, you will be at the end of a cycle so you'll feel good. Don't bet on it though, the chances of someone waking you up right at the end of a cycle is pretty low.
THE WHOLE POINT: The whole point is that even though most people need a particular number of cycles which add up to 8 hours (hence they say "You need 8 hours of sleep minimum"), it doesn't mean YOU need the 8 hours. Everyone is different and there are a few famous people who only need a small amount of cycles in order to replenish their energy, therefore they only sleep 2-3 hours daily which is phenomenal (imagine all the time saved). A cycle usually lasts 90 minutes, so just remember, if you wake up at the end of one, that's when you'll feel like a king. Your body might need 5, 6, 7 hours... You never know... If you naturally wake up earlier than most people (without interruptions), that will mean you need less cycles than most people. In that case, there's nothing wrong with you, you can just get up and enjoy a longer day .
Side note 2: Even if you woke up after 1 cycle (90 minutes), you would still feel energetic even though your body definitely needs a lot more cycles in order to engage in important activities such as muscle growth. Waking up & feeling good isn't everything.
SO HOW DO I KNOW WHEN I'M SUPPOSED TO WAKE UP?
This is easy. You need to eliminate all possible external sources which can wake you, including the urge to pee, so just drink water slightly earlier in the day so you urinate before bed. If there are no interruptions, your body will automatically wake you up at the end of your very own cycle; that's when you should get up.
For the next part I'll be using wikipedia to slightly help me out with the numbers, read only if you're REALLY interested :
*** More Scientific Part ***
Types & Percentages of Sleep In Stages:
• Stage 1 & 2: Light sleep; together, these two stages account for 50% of all sleeping time.
• Stage 3 & 4: Deep sleep; together, these two stages account for 25% of all sleeping time.
• Stage 5 (REM stage) – this stage represents the remaining 25% of all sleeping time.
Stage 1: Our heart rate and breathing become slower. If something wakes you up during this stage, you can easily believe that you haven’t fallen asleep at all as you are still highly aware of your surroundings.
Stage 2: This stage defines the beginning of true sleep. This is also the stage in which most people loose their awareness. The muscles become relaxed and the body stops moving.
Stage 3: Similar to Stage 4.
Stage 4: This is the deepest stage of sleep. Blood pressure drops; heart and breathing rate are decreased and stabilized.
Stage 5 - Rapid Eye Movement (REM): This is a special stage of sleep during which our brains become extremely active. Blood pressure increases, breathing becomes faster and irregular. The eyes start to dart back and forth. Most of our dreaming occurs in this stage. Because we might hurt ourselves while trying to move in response to the content of our dreams, the brain completely blocks our muscles.
The above 5 steps I copied ages ago from a legit site but can't remember which one, now I just edited them and rewrote them so they're more understandable. Don't be surprised if you recognise them. The rest is purely written by me.
I hope you've enjoyed reading this; just thought I'd share some useful information.
Edit: A source that slightly helped me:
Edit 2: By the way, interruptions may include vibrations of some kind, scary dreams, erections, people waking you up, wanting to urinate, traffic noise, the "biological clock" etc. I studied and experimented with these things carefully a while back as I was greatly interested in sleep cycles, that is how I know everything.
Edit 3: If a cycle is broken (disturbed) and you go back to sleep, that cycle will NOT continue. A new one will begin.