What happens if I do not eat for 2 days?

I did it last December.

The fasting started at midnight of a Thursday so the first “lunch” that I skipped was the Friday breakfast and I went on until Saturday at Midnight.

The first 24h you will feel a slight (albeit persistent) sense of hunger but physically and mentally you will be fine (almost 90%, I would say).
I recommend you to drink abundant water (+ an espresso when you feel a bit sleepy).

The second day (the Saturday) the sense of hunger subsidizes a little but you will feel increasely tired and it will take you a bit longer to do simple tasks and also focusing on certain things.

Unexpectedly I had to work very hard that second fasting day because of an emergency at work (I had to walk a lot bringing some heavy stuff to some places and also focus to write some long work-related emails) and, as a consequence, I got a very strong head-ache + strong sense of vomiting which I can only link to the fact that I was fasting (and not drinking enough of water).

I interrupted the fasting after 48h.

By the way: fasting for 3 days (72h) is recommended to reboot your immune system: Fasting triggers stem cell regeneration of damaged, old immune system