Testicular Pain in Nightmarish Dream

So, I've been having dreams ever so often where I wake up in my house (Completely accurate layout) and get out of bed where everything is dark and i walk out into the hallway, maybe to another room and whenever I realise that it's a dream I get confronted by a dark silhouetted figure that grabs hold of me, In a struggle it forces me to wake up. Occasionally in those dreams during the struggle, it's as if he's grabbing my testicles where the grip gets harder and harder (or at least in the groin area) In the dream the feeling is SOOOO F%$%# BAD it forces me to wake up suddenly. Once the dream ends however, my lower area isn't in pain. I've been having those sort of dreams where I walk out into my House in darkness and get grabbed by something ever since I was a little kid, minus the pain in the groin part. I've noticed I'm not the only one that gets these testicle pain dreams by google searching and finding stories that pretty much match what's happening to me, but never really an answer to why it happens.