I find labels like "hallucinatory" are often misapplied, but I found Gravity's Rainbow to be the one book I've ever read where it really applies because it immerses the reader completely in its universe.
Hallucinations are logical! They are complete in themselves and internally consistent. A closed realm that can't be challenged. And precisely there is not anything in Gravity's Rainbow to offer an escape from its mad world. Compare Swift's Modest Proposal: there are a few lines in it which 'escape' its mad world. Pynchon refrains from the least wink at a world other than the one the book offers. I only read it once and it deserves several readings. But I think there are 'episodes' in it which begin quite innocently and "realistically," then as you follow them, suddenly you are in an impossible world that is fully coherent in its own terms. Quite wonderful.
Carrol