Involuntary Contractions but no Pleasure

Today I used my progasm. I put it in and did "nothing". I focused on it being there, and anything I like about it, and after about 5 to 10 minutes, my progasm started moving by itself. Not hardcore but gently. I enjoyed that, but it was not pleasurable (meaning, I like it when it moves, but I did not feel any pleasure originate in my penis or prostate, I did not even feel my prostate!).
However, my penis was throbbing during these contractions. Each time it contracted by itself, I felt my penis move a bit, and that was also enjoyable. The best way I can describe it as, my penis was throbbing up, every second or so. Unfortunately, it only lasted maybe two minutes, and my throbbing, and I think my contractions stopped.
Is this a "good" sign?
For how many minutes must this throbbing continue until I feel something? Even a tiny feeling in my prostate.