A Hallucination is defined as perception of visual, auditory, tactile, olfactory, or gustatory experiences without an external stimulus and with a compelling sense.
During a majorly of Season 7, Sam, with the "wall" broken in his head, was having intense hallucinations of Lucifer, which had gotten to the point where he could neither sleep nor tell the difference between the reality and his hallucinations.
Here, situations and occurrences of hallucinations are briefly documented.
- Lucifer - He used this ability on Nick to convince Nick to say "yes" to possession. He did the same again to Vince Vincente.
- Horsemen - War induced a small town, making the inhabitants see demons, until his ring was removed. Ellen, Jo, Dean, and the townspeople were confirmed to have been affected by it, though presumably everyone was affected.
- Djinn - Monsters which are able to infect humans by touch which cause the victim to experience incredibly realistic hallucinations, capable of convincing them that they are in a perfect world or confronting their worst fears.
- Wraiths - These monsters can cause effective hallucinations with a simple touch. They have used this ability against Dean Winchester, Sam Winchester, and Martin Creaser.
- Hellhounds - When close to their prey, hellhounds cause their victims to experience hallucinations, so as to frighten them out of hiding and leave them defenseless.
- Buruburu - Luther Garland infected the people responsible for his death with ghost sickness, including Dean Winchester, forcing the latter to see hallucinations of Azazel and Lilith.
- Werther Box - Causes whoever fails to bypass its security defense to hallucinate. These hallucinations will drive those afflicted to commit suicide.