Epic start then nothing…

I normally take 1-2 hour sessions with a slow build to maybe a dry orgasm or two.
Today when I put my progasm in I had an immediate erection and throbbing muscles with a very sensitive prostate. Then bam; nothing. I kept it in for another hour but didn’t feel much after that first initial and amazing 3 minutes. Weird. Any ideas or insights as to what might have happened?