Yes. This is something worth keeping in mind. Even without going into DID in detail, the book operates off a pop-culture view of mental illness. From what I remember, Jack’s behavior is more in line with a schizoaffective disorder than DID.
But, even then, this is not how mental illness works. It does however add an element of discomfort to the book. Which is intentional. I said, in passing, that Fight Club is a book that needs to be read critically. I mean that. Palahniuk is a very provocative writer. Literally, he seeks to provoke a response.
I’m actually going to step back a little and say, in broad strokes, Fight Club is not a book you should enjoy. It is a book that should make you stop, and think about what you just read. In many cases, it’s a book you should disagree with. And, near as I can tell, that’s actually the authorial intent.
This is a book designed to get you talking, and get you questioning what you just read. Not a book you should endorse.
It’s worth noting that Palahniuk’s own experience with mental illness was insomnia. That informs his perspective and how he approached the novel. As someone who’s suffered from bouts of insomnia over the years, his insights there are on point. It’s not analogous to the characters he’s writing, and it doesn’t excuse the book of anything. But, if it got you to start talking, it did something right.
In direct response to you, I think Fight Club accurately reflects the way society perceives and stigmatizes at mental illness. Telling people to turn it off, and pass for normal. Within that context, it’s arguing that doing so is inevitably destructive, or at the very least self-destructive. Not the reality of how mental illness functions, but the subjective sensation of being marginalized because of it. I’ll admit, it’s not an easy subject to broach.