I Think I Pulled My Hamstring

I'm not joking. I was doing strides, rather I was building speed into my first stride after my run last night and suddenly the outside middle of my right hamstring went from fine to not fine in the fraction of a second. I know why sprinters stop now instead of finish the race, it's fairly painful. Mine isn't so bad, I can walk without a limp, but it is serious, I probably won't be running today.