(Spoilers ahoy for those of you who skipped to the comments section for some weird reason. Read the story first!)
When I wrote this novella years back, I did a lot of research on hallucinogens that could feasibly produce the bad trip Noelle suffers throughout the story. In addition to any articles about deliriants in general (mainly datura and its relatives), and even talking to a coroner through email, the majority of my research involved reading forum threads where former drug users shared their stories about bad datura trips, the terrible things they experienced, and the terrible things they did to themselves (or stories they read about others who used the stuff). In one story, a young boy drank datura tea, which kicked in a couple hours later: he quietly disappeared into the family garden for hours, and when he returned, he had castrated himself with the pruning shears. That's an extreme case, but there are similar cases like it, and tales of minor freakouts as well: hearing disembodied sounds, or having conversations with close friends/relatives who aren't there. It's scary shit regardless, because it leaves you incapable of discerning fantasy from reality, and nobody ever has a positive datura trip story to tell.
Based on my findings, I got the strong impression that a person's emotional or psychological baggage can influence the hallucinations, and the afflicted person's reactions to those hallucinations. So I wouldn't recommend anyone try getting high on datura, mostly because there's no such thing as a good datura trip; but I especially advise against using any psychadelic drugs if you have severe depression or other psychological baggage, even under supervision.
Then again, I'm not a doctor, I'm just a writer who thought the subject was interesting enough to write about.
So for anyone who was disappointed by the ending: the fact that the monsters were hallucinations and not tangible doesn't make them any less real. They were always there, lurking inside Noelle's mind and soul, waiting for a chance to get out. We all have similar monsters inside us.
This has been a sleep-deprived and borderline pretentious supplemental by Mike MacDee. Good night, and good luck.