hi i had gone through your query and understand your concerns. i would come up with two possibilities,
1.the first one may be,CERVICAL SPONDYLOSIS;due degenerative changes in the cervical spine
which compress the nerves and decreases the circulation may produce this condition.
x-ray for cervical spine may confirm the diagnosis
2.second possibility is,THYROID COMPLAINTS;check your blood test
for thyroid profile may confirm the diagnosis whether it is hypothyroidism
there is another possibility like ANEMIA
check your Hb levels for confirmation.
I hope this is helpful for you, thank you