What Could Be Causing Extreme Weakness In My Legs And Feet From The Knees Down After Napping, Which Improves With Movement?

Lately when I get home I ve been extremely exhausted and so I will lay down for a nap. But when I wake up my legs and feet feel extremely weak from my knee down to my feet, not so much above my knee. This goes away after a while from moving my legs and feet but upon waking, the weakness is almost unbearable.