explosive ending and strange spasmming session

I had a even better session last night.
My butt was craving all day after my last post so I saddled up again.
Got to dry O zone again and rode that for a hour or so.
I think it was about 2 hours in and I started to get in a frenzy and I could feel a massive build up of energy starting.
It got greater and greater until I was almost about to explode some how but I dont know how.
Alas the expectations or something got in the way and it subsided :)
I did not giveup but instead of the build up I couped something different.
I have never read about it before either.

I had a start of a build up like before but only slight and then the aneros dug itself in hard and clicked into place like what I call a dry O and then like the ejaculation felling of the dry O or a kegal thrust I went into some sort of spasm.
My body started spasming like a kegal at around 2 thrusts a second. Just the PC muscle.
It kept going like this constantly for I estimate 3 or so minutes!
Every now and then I might miss a thrust but it just kept going?
There was pleasure but a lot of energy was beeing put into it at the same time. There was a feeling of it building my arousal but not to anything huge.
After the 3 minutes or so it stopped and just went back to anal twitching.
I was buggered and went to sleep. Woke a few times through the night with miss helix teasing me a bit.
In the morning I removed it for a pee and then reinserted but with the eupho instead and had a few dry Os and then decided to call it quits.
I was so horny still I decided to have a super T.
It was a massive build up and as I came I squeezed so hard The eupho shot out half a meter away from my arse onto the bed! :(
It was a bigger load of cum than usual.

I dont know what was happening with the spamming.
Has anyone else experienced it?

Overall it was my best session ever that I can remember.