Truth is usually represented at a bright light in everything I've ever seen. You could always do the whole book theme, but that's usually knowledge, not necessarily truth. As for mental illness, you could make something up. I imagine a human head with two arrows chasing each other in a circle above the head would work. Unfortunately I don't think there is a standard symbol for mental illness, so the best you can really do is just make one up. I'd go for the whole bright light to represent truth, though. It kinda goes with that whole enlightenment idea. ~JKS