What Causes Fingers, Arm, Face And Legs Numbness With Rigidity?

Hi, the other day I was in an intense power training workout. and after, while driving, within a Mile my fingers went numb and then my left arm, then face and then legs. I stopped my car but within a couple of seconds my hands, fingers, arms, legs, ankle all went rigid and straight. i couldn't move. I had somebody get me a coke and chocolate and in 15 minutes i could stand and walk. This seems very strange to me. I have heard of numbness but the rigidity i experienced was something weird. could there be another cause like a potassium deficiency? and is this something that could be life threatening?