Legs go out on me

The symptoms of whatever is wrong with my legs started about 5 years ago, and has only happened about 15 times during this period. One of which involved a seizure of sorts afterwards. I can be walking, stepping out of a truck, running, or anything and my legs will go numb as if I can not feel them and go stiff and sometimes jolt or shake uncontrollably. This seems to happen when I get "excited" or stressed or am put through some sort of anxiety. It happens randomly also though.

I was boxing with a buddy one time and not hitting in the head at all and hardly hitting hard, and my legs went numb and started shaking, and I can't remember anything after that. I apparently had a seizure, but the Dr. said I was not epileptic.

Other times I'll be walking and my legs feel like jello and may or may not go completely numb, in which I fall to the ground. The other day just one of my legs went completely stiff while jogging and became a "peg leg."

Does anyone have any ideas of what this could be because it worries me that there could be a more serious underlying issue that may progress. Thanks a lot for your help.