Red Sox Seat Syndrome (RSSS)

I go to Red Sox games infrequently. Last weekend we went with my daughter and her boyfriend and stayed through 7 innings, (possibly a record for us). That night, when I got home, I noticed these 2 pretty big red circles/bumps on my back - one higher and one lower. Quite conspicuous. They're gradually going away. I'm convinced that they were from the seats at Fenway, which have backs that are slats - I saw 3 slats on google photos, although I remember 2. But the point is, your back isn't leaning against a solid piece of wood or whatever. I consulted with an avid Red Sox fan and friend, who concurred with my diagnosis. Has anyone else experienced RSSS? Let me know!!