Something happened.. not sure what?

So this will be my second session. After about twenty minutes on my back I didn’t notice any changes other than a slight pulse in my hole. I decided to turn on my stomach as that’s how I usually fall asleep so in turn I became more relaxed. After 15 minutes I noted the pulse in my anus got stronger and an increased building sensation began.I let it build up and immediately knew something was different because my heart started racing immediately. It only lasted around a minute and felt nice. I had some mild shaking. It was definitely something but I’m not sure what it was? Is this a P wave? How do I continue these and how far away from a Super O is it? Any feedback? Thanks!