I once was dreaming that I was flying (extremely rare for me).

Then I realized that geometry was glitching out, things weren't smooth, there was just too much in view, and I could see everything, to the smallest leaf of every single tree at once, all made out of 3D vectors and particles not geometry, it was all particles; eventually the dream collapsed and caused me sudden sleep paralysis as my brain went into hypedrive and killed the process with an error code I can't remember; a nightmare is tame by these standards.

The experience was awful; honestly; but you can probably run doom, but everything will feel real, it will be your reality; you will get PTSD if you could run doom.