Polygraphs may be foolproof, but they're not crazy-proof. If you honestly believe your hallucinations are real, well...

They're also not very smart-proof. There are all sorts of ways to fool a polygraph; it measures stress levels, not truth directly. Some people have conscious control of their blood pressure and even heart rate. Of course, if you put a tack in your shoe so you can poke your toe on the calibration questions, you can skip all the meditation and focus.