Psychosis: When you lose touch with reality and see, hear, or believe things that aren’t real, doctors call that psychosis. You may have delusions. That means you hold on to untrue or strange beliefs. You might also have hallucinations. That’s when you imagine you hear or see something that doesn’t exist. Psychosis is a symptom, not an illness. A mental or physical illness, substance abuse, or extreme stress or trauma can cause it. Psychotic disorders, like schizophrenia, are mental illnesses that involve psychosis that usually happens for the first time in the late teen years or early adulthood. Young people are especially vulnerable for reasons doctors don’t fully understand. Even before the first episode psychosis (FEP), they may also show subtle signs of behavioral changes. This is called the prodromal period and could last days, weeks, months.or even years.