When I used to feel like that it was due to sleep apnea. I just never fell into a deep sleep and was never 'refreshed'. But, before you start to think that there is something wrong however, try fresh air and exercise. Even opening the windows can help. There is some merit in the old adage of 'blasting out the cobwebs'. I have routines to move my old bones and put some air into my lungs, opening the garden shed to air it, watering the tomatoes and herbs, taking all the rubbish to the bin etc and I do them all before having a cup of tea or coffee.