I was sighting in one for a customer and was holding it in the offhand as I held an M-16 in the Marine Corps. Doesn't work that way! I was lucky enough to just get by with a lot of pain and some numbness for a while. I've seen this happen a lot with crossbows. Please be carefull. Always look at your fingers before you shoot!
That looks like it felt great. Ouch man. Hope it heals up ok. Did you see a doctor?