I'd say since it happens when you try to walk, it's coming from either your foot or your back. I have severe back issues and have for years. After my numbness started in my foot I thought it was from the chemo.

I'd lie in bed and do different things, like bring my right foot high up on my other leg that was drawn up, and when the position of my back changed, I noticed the feeling trying to come back. I ordered this cream and I really think it's working. I've also fallen several times too so I'm sure I jarred things in my back. My foot issues didn't start until after I slipped off the outside steps and sprained it. I did not seek medical treatment for it though.