Involentaries

Today i experienced something that felt like butterflies in the stomach, a really weird feeling when you're not in control of your own muscles. I've never experienced major involentaries, leg movements, shaking, abs contracting etc before, but i've had minor ones in the groin area that are always kind of moving around.

I'm curious, is it a sign that i'm close to a orgasm when things starts getting out of control, when do you usally get your major involentaries? Do you have to trigger them somehow? I've read about people trying to exhaust their muscles by clamping and then go into cramping/invols.

Is there perhaps some technique involved to trigger involentaries, or do they just happen?