numbness in feet

I'm working my way through the book, and it's brought quite a lot of relief. I stretch lie before I go to sleep, and I'm sleeping deeper and more soundly than ever before.I also do stretch lying again a few times soon after waking.

My problem is this, and it has been with me ever since I got a herniated disk in my lower back a year ago. I'm OK when I get up, but after I leave the house and start to walk to work , a 45 minute walk, within about 500 meters  my feet begin to get very numb and my front leg muscles begin to hurt. I can  relieve this by  stretching my legs like runners do two or three times. There is also the base of a statue I sit on for a few moments that is the perfect height to relieve the numbness. After stretching and sitting there for a few moments, the numbness often goes away completely, or at least subsides to tolerable levels.Once I am sitting down it goes away and generally doesn't come back to bother me during the day or when I am walking home at night.

I'm wondering if I am doing something wrong in stretch lying or in the position I am sleeping in?