Comment by UltraSane

I have never used hallucinogens but know people who have and one of them suffers from Hallucinogen persisting perception disorder which causes visual snow or noise in his vision. It is a bit like visual tinnitus and he says it greatly reduces his quality of life. Wikipedia has a animation of what it looks like

https://en.wikipedia.org/wiki/Hallucinogen_persisting_percep...