I've been searching for a diagnosis for 2+ years. I thought it was probably ME/CFS, but as my illness has become more severe, I'm less sure. For the last 3 months, I've been dealing with flare-ups of severe muscle weakness in my legs. I used to bike to work, 3 miles each way. Suddenly, I couldn't even walk one block or climb one flight of stairs. At times, I've been using a cane to get around my house, but my doctor thinks I need a walker. The problem is specific to my legs, and often comes with tingling and slight numbness. I had an MRI, and EMG, and a neurological exam - all normal, except for some hip weakness in the neuro exam. It's hard for me to tell if it's true PEM, because there is often a delay between the exertion and the crash - I've become good enough at staying within my energy envelope that I rarely push myself into crash territory in one day, but if I overdo it and don't schedule enough time to recover, a crash can come days or weeks later. What confuses me is that these symptoms are so specific to one part of my body. It seems to be happening in response to me using my legs too much, and then I feel the crash mainly in my legs. It doesn't have a huge effect on my arm strength, and doesn't always come with the need to lie down. This is really odd to me - in the past, my crashes were a full-body thing. Have any of you had this experience?