Agree with DLD, it happen to me too a couple of time but it was more when I stretch rather then jelqing. I quickly pacnicked and came here to check. this forum is your best source of information you can find pretty much every answer, so next time don't panick.
As DLD said by stretching or jelqing with a strong grip you can have a small cut in one of the small veins, we all know the penis is full of such vein and some of them are a bit too weak or think hence why we have sensitivity in our lil brother.
give it a day or two to rest and now you know your limit on stretching so don't push it. by stretching way over you are going ot hurt your self and it is not going to speed up your gains on the contrary, it will short them because yuou will have to take day rest.
Listen to your body and don't push it to its limit. and dont foget warm up more