VALIS is a full-fledged acid trip. There are pages where the narrative changes perspective so harshly it can break your brain. Recommend the trip regardless.
e.g., remember when Horselover Fat gets beamed secret information from a faraway satellite through a pink light to his forehead? Or when he learns we are secretly still living in first century Rome? Both things that PKD actually believed happened to him.
The lucidity with which PKD explored his mental illness in VALIS is pretty extraordinary.
Have you read How to Build a Universe That Doesn’t Fall Apart Two Days?
Check it out