The very short answer is that the film's director, Anthony DiBlasi has openly stated that he wants the audience to be conflicted over whether what Officer Loren is seeing is real or imagined (and would presumably be very pleased to see that it worked!).
At that end of the film our hero has been subjected to numerous instances of seemingly supernatural events; being attacked by undead creatures, repeatedly scared by people who subsequently disappear. On top of that, she also seems to be suffering from borderline psychosis brought on by stress and lack of sleep.
The fact that she experiences a "moment of clarity" at the end (when she realises that what she thought was a Satanist cult was in fact the HAZMAT team) which would imply that the ghosts were in her own mind, but that's just my opinion.
DC: In the film there are instances of Satanic activity, claustrophobia, and a ton of jump scares – what is it about this movie
that’s going to scare the crap out of people?
AD: I think the main component of it is that you’ve essentially got one character that takes you on a journey, and you’re in her point
of view through the entire movie, and I think that helps a lot for
viewers to just settle in and experience everything as she does.
Every corner that she lurks around, there’s something waiting for her, and it’s always in her point of view – is it just playing with
her mind, or is this a full-on haunting? It’s a really important
element of the film, just keeping that momentum going for a fresh