One time, when I was working at a summer camp as a specialty staff, my coworker/roommate who I barely talked to and barely knew randomly pulled out his switch and asked me if I could do a part of Celeste he was stuck on. I said sure, and did it for him, but then asked why he asked me in particular. He just said I 'seemed like the type of guy to have beaten Celeste'. I haven't started socially transitioning, so I don't know where that vibe came from, and I still think about it 
When I was growing up I was sleeping one night. I woke up, and CLEARLY heard a voice shouting gibberish at me. No idea ¯_(ツ)_/¯
Hallucinations are relatively common and most of the time aren't connected to any mental health issues or problems at all. There's a group called Hearing Voices Network if you're curious that does education and advocacy. There's a huge stigma about it but most people who experience audio and visual hallucinations have really mundane, harmless ones and it's pretty rare for people not to know they're hallucinations. It's one of those things that isn't a big deal but there's so much stigma about it people are afraid to talk about it so no one knows how common it is.
Personally I think we're so hyper-tuned to be listening for language and seeing potential threats, friends, and food, and our perception of the world is based on so many kludges and hacks and barely functioning systems, that most hallucinations are just false-positives. Your brain receives white noise or an ambiguous sound and interprets it as speech or whatever out of an abundance of caution.
my first halucinations really stuck with me for a long time until i had more & now they're kinda forgettable