Blood in ejaculate

Night ago I had sex with my girlfriend. I didn’t use protection, although I have to emphasize that she was pretty rough. The next day, my ejaculate was reddish. My penis doesn’t burn; I don’t feel any pain or anything like that. Basically, beside the blood in my ejaculate, there are practically no signs that something is wrong. But still, this is rather frightening experience and I have no idea whether I should panic or wait a couple of days to see if everything will go back to normal.