What Is The Treatment For Numbness In The Legs?

Many times when physically active, (especially running with high knees), it seems like my legs sort of give out. For example, I may do an exercise where I run in place, with high knees, and then jump in place. Many times during this, after I run for a little while, I kind of feel "light-legged." Sort of similar to when you stand up really quickly and your head barely feels attached to your body; my legs get a similar feeling. Usually after I notice this, my legs momentarily seem like they try to keep running, where as I'm trying to jump, causing me to stumble and/or fall. It's as if I lose control of them for a short moment.

Any way you can help?