I have Churg- Strauss Vasculitis- which I have had for 16 years. My legs go numb from the knee down whenever the mood takes them. Strange as it sounds I then have excruciating pain in the backs of my knees. I have no triggers and I can be woken from sleep due to the numbness. Standing, sitting lying down makes no differecne I get ferocious tinglingling as a warning. cold can make them go numb too. I caan't be the only one that has this problem to contend with!