A common problem for sure , you are not alone.
I think we all know it is most likely the circualtion being interrupted by being in certain postions for longer than normal . In sleep we can tie our limbs and bits in knots here and there. Also any neck problems often call this when lying down in different or familiar positions.
Aged souls feel it more maybe beacause we are not as rested from our days? We just zonk out?
I find it cold as well as numb and, do a lot if flapping to reactivate the blood there. eeeks! Creepy stuff.!
But the worst for me now is when I raise upright from a lying position or sit too long in one place, the positional pain of my readjusting tail feathers, I then feel very tingly (and painful in buttocks and back of thighs) numb from the waist down to my feet.. now this makes for very awkward moving and walking, or to bathroom visits..it lasts about 15 -20 minutes before I feel safe upright again..pressed nerves .Then when 'adjusted' snd it wears off, off I go again racing, the old hen running clucking as usual..yep!!.
Not sure the last needle did any good methinks it added more..bugger!