You come upon a person who has a flushed face and is claiming to hear noises that you cannot hear. the person initially is calm but then suddenly becomes quite upset and agitated. you suspect that the person might have abused or misused which substance?

This person has most likely abused a hallucinogen like LSD, ecstasy aka MDMA, or something like that. But the overall answer is that they misused/abused a hallucinogen.

Fun fact: The person who invented ecstasy was Anton Köllisch. 
(That's a picture of him, I don't know if he was that young when he made it though...)