I Was Swinging From My Hands On A Coldish Day

I was swinging from my hands on a coldish day a few days ago and shortly after the back of my hands started hurting when I had them at my sides. I have noticed that there is a swollen vein (not entirely swollen, just some parts) on the back of each hand that is where the pain is. If I rub the vein it hurts but the swelling goes down for a bit. The pain isn't sharp, more like a throbbing. I just don't know what this means or how to train so that it doesn't happen again.