Can't stop

Out of the blue, I felt like watching some porn. So, I turned in the computer, pulled up Redtube. I start watching and after about 5 minutes, I feel the need to get off. I stuck my hands inside my panties and rubbed my clit for all of 5 seconds. The next thing I know, I'm cumming and I can't stop. What the fuck is that about? I keep having these back to back spasms. Don't get me wrong. I love to cum, but this has never happened before. It's kinda freaking me out....in a feel good kinda way.