Does this ever happen to you durring your session?

I have been using the aneros on and off for a couple years, sometimes going months without using. This is because I have never had a super O, and a traditional orgasm with aneros inserted doesn't feel comfortable, it kind of ruins it. Anyways.

I have been using the mgx one or twice a week lately. Today was good because it was mostly involuntary muscle contractions which for me was exciting because I always feel like I'm getting closer to the elusive super o, even if I'm not, the fact the aneros is moving on it's own gives me hope.

Well about 30 min into the session I began holding my breath, and my body began kind of flexing. This went on for 30 seconds to a minute and I realized durring that my body was acting like I was having an orgasm. Only without the pleasure, ejaculate, or feeling of release, or relief. It was kind of frustrating actually. Afterwards I started to feel a little sore and felt it was time to stop. Is this normal, or just a random event? Or is this a sign my body is warming up to prostate massage?