Hallucination is a perception that occurs without an external stimulus, meaning a person experiences something that isn't actually there. This can involve seeing, hearing, feeling, or even smelling things that do not exist in reality. Hallucinations can happen to anyone but are often associated with certain conditions like schizophrenia, bipolar disorder, or severe depression. The causes of hallucinations can vary widely, including mental health disorders, substance use, or extreme fatigue. They can also occur in medical conditions such as dementia or Parkinson's disease. Understanding the underlying cause is essential for effective treatment and management of hallucinations.