I do not have any serious medical condition that I know of. Sometimes when I wake up, my left leg feels as if it doesn't exist, or is made out of jelly, when I wake up. It has resulted in some pretty tough falls 😁😁. My right leg feels perfectly normal, but when I try to step with my left leg, I just stumble and fall over. Could it be due to hypnic jerks I get sometimes?
Very probably not.(1)
This sounds like an issue with nerves (especially a pinched nerve) that makes your Brain unable to "proper" communicate with your leg, hence the jelly-like feeling.
However, I would expect your leg to feel numb or "pins and needle" pain. Not feeling your leg in the morning seems normal to me (i.e. paresthesia), but falling because you don't have control over your leg seems rather serious.
If this does not go away, or if you do feel either pain or numbness in your extremities, I would highly advise you to consult a doctor.
(1): I can't rule it out with 100% certainty as I neither am a professional neurologist nor can I examine you thoroughly, but with very high chance sleeping habits are not important. If you are however convinced to be suffering from paresthesia every morning, this might be cause by a weird sleeping position which is applying a lot of pressure to your nerves.