There could be many reasons for this, but one possibility is that you have undiagnosed sleep apnea. The "sleep" of someone with apnea is not a restful sleep -- it is interrupted, over and over, possibly a hundred or more times, by a cessation of breath and an (unconscious) jolt from your brain to wake up and take a breath. You are not aware of this. The result is you never fall into the deep sleep that is truly restorative and wake up tired, exhausted. Do you have a bed partner? Does he or she notice this lack of breath and this sudden snort? Or if you sleep alone, turn on a recorder that can operate for several hours and play it back.