I think I've watched every episode thus far
Regarding the most recent episode, "Fear", I don't know that I thought of their hallucinations so much as "fears" as they seemed to be issues related to past guilt's, trespasses. Most have already been revealed and so far the only one who seems guilt free is the dorky guy (I don't know his name, but he's always seeming to putting Paula down and last episode before "fear" his klutziness lobbed off Paula's thumb.
The revelation I found most interesting in the "fear" episode was Nadia's hallucination; hers appeared to be a male version of herself. Since the hallucinations seem to be specifically relevant to each person having them and given Nadia's preoccupation with sexual exploits, I wonder if she is compensating for her insecurities through sexual conquests. I also wonder (based on the appearance of her hallucination) if she may be a post-op transsexual.