When I wake-up (i.e. hear the alarm clock and open my eyes) I experience severe muscle fatigue, that I am hardly able to force myself to move my arms and legs to get-up. I feel like my muscles were extremely weak at that moment, and I also feel pain in them. It feels so bad and weak, that half of the time I am not getting out of bed, and sleep another few hours, although I already had enough sleep, and it doesn't feel any better after the extra sleep - in fact it feels worse.
When I do finally manage to get out of bed, the muscle fatigue and pain magically goes away after 15-30 minutes, and during the day I feel completely normal, full of energy and fine.
It doesn't matter if its after a 2-hour nap or a long 8-hour sleep, its the same fatigue. And I am not feeling sleepy, drowsy or anything like that, I just feel my muscles are extremely weak. I am skinny, 60 kg, but slowly gaining weight, in fact I am tracking my food intake and making sure I get at least 2850 kcal each day, so I have enough energy source. And during the day I am not feeling the fatigue or energy-less, its just right after wake-up.
What might be the cause of this?
EDIT: more info:
I measured my blood pressure immediately after wake-up. It was 77/37 mmHg. And that is an average of 10 measurements taken in the 10 minutes after wake-up. That's somehow low, isn't it?
Not that my blood pressure normally during the day is too good, it is on average something around: 95/62 mmHg. After riding on bicycle for an hour it is about 103/64 mmHg.
Can that have something to do with my wake-up fatigue? What can I do to get my blood pressure to some normal levels?