Theres 2 things that can happen with nitrous.
You become oxygen deficient and do serious damage to your brain. This usually requires doing back-to-back huffs, and fully exhaling. Your lungs dont sense the absence of oxygen, they sense the buildup of CO2 so if you fully breathe out, then take a huff, you wont realize you arent getting oxygen and feel fine, when youre actually very oxygen deficient. Best way to fix that is by only breathing out half way, and doing a few deep breaths before and after.
Vitamin b12 deficiency, but you need to do A LOT for this to be a thing. There are people out there with one of those 5 foot gas cylinders filled with nitrous and they just go all day. Those are the people who need b12 supplements.
Its not nitrous.
Dont try to use automotive nitrous, its been denatured.