What are these contractions?

I have had my MGX for 8 months or so and I have become addicted. I prefer to use it in the mornings as this is the time when I have the most energy. I have decided to take the advice of some of the forum members and only use it every other day.

This morning as I awoke I could feel my prostate sort of buzzing, and it was my scheduled day off from the MGX. I rolled over on my side and began contracting the various sets of muscles that I use during an Aneros session. After few minutes of contracting the schfincter muscles I experienced a contraction of what seemed to be all of my large muscle groups, arms, legs, back, chest and thighs. I worked this muscle group several times with the same result, it felt good, and I felt like I was in a little better place afterword than before I started.

Can someone explain to me what I have experienced?