Hallucination horror stories don't just result from bad trips. In addition to drugs, hallucinations can also be caused by mental illness, the side effects of medication, or sicknesses such as fevers or flus.
While some people see nice things like rainbows or elegant fractals, many others report terrifying visions. Severed body parts, dead babies, and large insects have been known to appear, and can often be quite horrifying, as seen in these stories from Reddit. Users may have been trying to expand their consciousness, but hallucinating isn't always a good time.
Psychedelics like DMT, LSD, or mushrooms can produce some pretty crazy stories, especially when users freak out during the trip. Some people who hallucinate have the capacity to realize what's going on, allowing for the sounds and visuals they experience to be thought of as a passing illusion.
Then there are people who are unable to discern between the real and unreal, making their hallucinations even scarier. While melting faces and breathing walls can be exhilarating, when demons and shadow-people appear, things start to get more terrifying. In these stories from Reddit, people describe terrifying things they've seen while hallucinating. Try not to freak out yourself.