I guess I had a p-wave

This was around my 6th session and had started to get some buyers regret. I looked up what hitting the prostate would feel like, cause I was wondering if it was even hitting it all, and started to focus on those feelings (generally the feeling that you have to pee).

I thought it was lower than the aneros was hitting because that's where a more intense feeling was coming from. I now think that's most likely something called the cowper's/Bulbourethral gland. After watching some porn bent over (didn't want to sit) I layed down and just relaxed. I tried keeping the aneros in the right spot.

After a while the feeling of butterflies in the stomache appeared and a shudder spread from there throughout my body. My penis got hard rapidly and it felt like some sort of ball was inflating around my prostate/bladder. it started tingling and my penis seemed to melt away. At some point it started shrinking I assumed it would return or something but I now had this feeling of a full bladder which just overwhelmed every other sensation which made me stop.

So I assume this was a p-wave, but anything else got stopped because of me needing to actually pee.

Any tips on how to prevent this form happening again? (I already went to the toilet before inserting the aneros)