Abby, I have similar short lasting weak spells and have had them since I developed MG.

I haven't had them for a few months now, but my experience sounds like the same as yours.

I can usually feel them coming on, I get tingly sensations in my arms, legs and face, as if I can feel the antibodies going outward from my chest...and I always know what it means, that I'd better find a comfortable place to rest quickly. Mine are usually triggered by stress or pushing myself too much. They go away in 30 minutes to an hour (I haven't actually timed it) after resting. I am left with a residual weakness afterwards, but at least after resting I can move around again.

Before I learned to recognize the signs (and possibly, this event happened much faster because was in worse shape, I'm doing better now) I spent a lot of time on the floor waiting for this sudden weakness to go away.

You aren't alone in this.

Take care of yourself.