I have perceived weakness and numbness in my lower legs, too.
I even have parts of my feet and stuff go numb out of nowhere when I am lying down....and sometimes, like you said, when I am up and around or even sitting in a chair.
I always freak out when it happens....
I happen to have weak ankles (it runs in my family).
But, I believe it to be associated with my Anxiety.
Because my nervous system has been shot since this whole Anxiety thing completely took over.
It is so scary.....cause I start thinking that I'm about to die of something crazy...but, I never do, lol.
I hope you get to feeling better soon.
Read some books on the connection between Anxiety and our nervous system....it's really interesting and it helped me to be a little more at peace with everything