Why do I wake up and still feel drained the entire day after a full nights rest?

This could be many things either physical or mental. Perhaps you are going to bed with things on your mind that aren't allowing you to get the type of sleep needed for the mind and body to rest and recharge. You aren't getting the Rem sleep needed.

Feeling drained can be a result of many things, such as your diet, lifestyle, medical reasons and depression. If you continue to feel drained for more than a few days go and see your doctor.

You may feel drained because of something other than how much or little you sleep. Tiredness and lack of energy is a symptom of depression so I recommend if your feeling of being drained affects your life in some way then I think you should talk to someone.

Sleep can be measured in two ways: quality and quantity. The full nights rest will leave someone feeling as if their should be getting the most out of their sleep, but the quality of the sleep is equally as important. Anxiety, stress, and built up emotions can all affect the quality of sleep. Maybe try to do some breath work before falling asleep to relax into your slumber.

Did u maybe see if you are getting enough sleep u could maybe try listening to relaxing music or reading a book or listening to the birds outside or do some medidation to help you relax before to go to sleep to try and get a full nights sleep. I find listening to music helps me to get a full night sleep and makes me work better and feel less drained during the day. You could also speak to someone about maybe helping you get a plan for activities to do during the day to distract yourself from being sleepy