Painal is simply and abbreviation for "painful anal" and may have an added description of being something the girl may like or at least enjoy because her guy enjoys it. There are sites on the internet that specialize in painal such as sinnistar.
He did not realize his wife enjoyed painal. He knew the anal sex was painful for her but didn't realize someone could enjoy painful anal sex.
When anal sex brings about extreme pain, typically with the first attempt but has been known to occur in sober women or she just can't seem to relax and let him do his thing.
Also used when referring to the first few minutes of anal entry.
In men, painal can be the excruciating pain that shoots through your rectum without warning, typically in a board meeting or social settings.
Mike and I tried butt sex last night. Once we got through the painal minutes, I loved it.
Or
Dude, I had the worst painal attack at my girlfriends funeral. My girl thought I was crying with emotion but really it was the painal contractions.