Sleep quality is affected by: 1. What you ate, drank, took, looked at night 2. Bed linen - the material from which it is made, the degree of "dirtiness" 3. Things in which you sleep 4. Temperature, humidity, odors in the room 5. Thoughts with which you fall asleep 6. The person you sleep with
When everything coincided perfectly, I kind of slept for 4 hours, but you feel like a funny bunny. Even if I woke up a little in the wrong phase. If something is wrong, then 12 hours will not be enough. You can, of course, download applications with phases, buy a highly intelligent alarm clock, but if the apartment stinks of fried potatoes, the blanket crawls out of the duvet cover and pricks, a liter of tea gurgles, fell asleep thinking "f ... bl ... nah ..." - you are unlikely to have a triumphant sleep.
One possible reason could be that you wake up during different phases of sleep.
Sleep consists of alternating phases of slow and REM sleep. In simple words, during REM sleep, our brain rests, its activity slows down, and during REM sleep, it is active, almost the same as during the day. During REM sleep, we have dreams. If you wake up a person in REM sleep, even if he slept for a long time, he will most likely feel overwhelmed, his brain will need more time to recover, but if you wake up in REM sleep, it is highly likely that you you will feel more cheerful, even if you have not slept for long.