Low back pain, radiates into left buttock and hip, down into left leg, sometimes all the way into the foot. Classic sciatica stuff. Mostly only hurts when standing/walking and at night when sleeping. The muscles in my left leg, especially left calf, twitch a lot.... I used to be worried about ms too, but turns out twitchy muscles are usually TMS related. Makes sense given the reduction in oxygen to certain muscles/nerves, as Dr Sarno explains. So I would imagine that's what is going on with you- a reaction from mild oxygen deprivation, resulting in pain, compounded by fear and obsessive thinking/examining of symptoms.