> "Drain" for an introvert can mean anything from starting a muscle tension clock that will eventually cause a headache to a straight-up panic attack that could take hours/days to recover from.

Unless you are being hyperbolic with your usage of the word "panic attack", having one during social events is not "being an introvert," it's a medical condition.

I am an introvert and have also had unrelated panic attacks. Panic attacks effectively paralyze you, you feel a deep and uncontrollable sense of doom, often accompanied by palpitations. Sometimes you feel like you can't breathe.

If caused by social interaction, that's not a normal thing to experience, even for introverts. That is in the territory of actual medical issues: panic disorder, social anxiety disorder, etc.