Do people hallucinate if they are overdosing on painkillers?

Possibly. I have seen patients on very high doses of narcotics and thinking clearly. There are also patients who are extremely sensitive to low dose narcotics. New blood tests are being developed to predict how an individual will respond to painkillers on the basis of their genetics. One thing is certain, narcotics plus other drugs such as xanax, (alprazolam) Soma or Valium will cause mental clouding in many people.