ELI5 - Why do you see “sparkles” after dry heaving?

For context, I have a daily medication that makes me super nauseous if I don’t eat something either right before or when I take it. When this happens I typically dry heave a few times (because I have nothing in my stomach) and 95% of the time I then see sparkly dots in my vision right after. Just curious as to what causes this, why it happens, and if it’s something with which I should be concerned. Thanks!! :) Have a wonderful day!!