Interesting fact is that I often had itchiness in this groin area (I shower every day and without soap, so I guess the itchiness is an internal problem, not from dirt or allergy or whatever). After orgasm, the itchiness is more intense.
I was at the doctor today because the bulge(?) at the groin came back. He confirmed it is inguinal hernia and recommends to do a sugergy in the next years (nothing urgent though).
I also asked about the lymph knot topic, he said it can very well be related to vaccination, but it's for sure a inguinal hernia and not just a random lymph knot. (He did some test where I had to cough)
Maybe predisposition to inguinal hernia is same as predisposition to POIS?
But I guess like you, it's probably random.