Newbie confused with the muscle spasms

I just got the Helix Trident, and have been using it for a few days. From my (limited) understanding, the relaxation of the muscles is what is supposed to build up to the super-o. And during the build-up, the muscles are supposed to involuntarily move. I had a recent session where I did have involuntary muscle spasms, but they were due to/during the contraction of my PC muscles. I think the muscles were too tired and my body started shaking all over. Is this normal?