A valuable lesson that I've learned is just because a patient acts crazy (or possibly IS crazy), you can't discount what they say. I offer two memorable examples:
When I was rotating in the ER as a med student, there was an old woman who had this crazy story about being locked in a basement by her family. The story involved tin foil hanging from the ceiling and all the things you'd associate with someone who was psychotic. But I later found out that when social services checked out the lady's house, apparently everything she said was true. It was a case of elder abuse.
The second story is one I heard from another physician. She said she had this schizophrenic patient who one day said that he couldn't walk anymore because there were "animals eating away his back." The guy was floridly psychotic and everyone kind of wrote him off.
Finally, they managed to get him in an MRI machine. Metastatic cancer to the spine.