After having sex i feel bit powerless in my legs, what could be the reason?

Neurologic Disorder: Any neurologic change is concerning. Possibilities include nerve compression of your spine or spine roots in your spinal canal, a nerve sheath destruction such as Guillain Barre syndrome, or some sort of actual muscular problem such as muscular dystrophy, or perhaps something else higher up in the brain. Timing is key-It would be important to be evaluated earnestly if this is rapidly progressing.