There are nerves that run from the spine all the way down to your legs (not sure if they're really long nerves, or if it's a group) but maybe you had a "misfire" that triggered the shock feeling running from that...umm...area, all the way down to your foot.

Every few weeks or at least once a month, I'll get a feeling like someone has shoved a taser into the side of ribcage, towards the back, and is giving me a quick zap or two. (and yeah, I've been tasered, so I know what it feels like)

It's not quite as painful as a real taser zap, but it's enough to stop me in my tracks to say "oy vey!", and make me look around for the taser.