What causes someone to zone out?

It is when the mind and ego cease to dominate our every thought and we just bask in a state of no thought without the constant running commentary of mid.
I don’t know the physiological reasons but I do know that this is the goal of meditation practice.

Being over tired, in some cases. You can’t go to sleep, for whatever reason, so your brain just takes a break.

Tired, and a lack of interest in a subject do it for me.

I “zone out” when thinking about something intensely. Everything else just falls away.

Thanks for the responses, but I’m looking more for a medical/biological answer. Just curious about the nature of it; evolutionary purpose, is there a clinical benefit, etc.

Low blood sugar. Or low blood pressure. Your brain needs fuel.

@RedDeerGuy1 I think you’re confusing ‘zoning out’ with being dizzy. Those two experiences are nothing alike for me.

Intense lack of interest.

I doubt there is a single physical or medical answer. It depends on the underlying cause. My grandson is high functioning autistic, and he has frequent episodes. When he was younger, we would tease, saying “Earth to AL”, thinking he just wasn’t paying attention. Once he was diagnosed, we stopped.