It sounds like the symptoms you are suffering from after activity or a lecture is overstimulation. For you.

It's been my experience that the symptoms or signs of overstimulation changed as I recovered and changed based on what was stimulating me or how bad I would get.

My voice and speech still get affected when I'm tired or overstimulated.

But I used to get a swollen feeling in my head or dizziness would increase or any number of other things could happen.

I suspect that the signs and symptoms for each individual may differ too. And that may be why you're having trouble finding a definitive answer about what it exactly does or how to identify it.

Pace yourself. If you start to feel an increase in symptoms, then slow down until the following day or until you recover from them and they diminish.