Psychosis is a common symptom in serious mental illnesses particularly schizophrenia spectrum disorders (including schizophrenia and schizoaffective disorder) as well as bipolar type 1 disorder. Psychosis can also occur in other disorders or even on its own in rare cases.

When someone experiences psychosis it esentially means that their mind has separated from reality. The real world is getting blocked out and some imagined world is taking its place. The two core parts of psychosis are delusions and hallucinations.

Delusions are any fixed-belief that has no basis in reality. “Paranoid” delusions are common in schizophrenia and include things like, believing that a terrorist group is hunting you or that you are part of a government conspiracy. Other paranoid delusions may be more subtle like a core belief that your family is “setting you up” or “out to get you”. Delusions of "Grandeur” are common in bipolar disorder and may include a belief that you are a descendent of royalty or have a supernatural power. More subtle delusions of grandeur may be things like a belief in unstoppable good luck (which can lead to problematic gambling) or a feeling of being intensely attractive.

Hallucinations are similar but they involve your brain actually perceiving something that isn’t there. Like the experience that you are literally hearing the voice some other person/being telepathically. Hallucinations in severe mental illnesses are often auditory (i.e. hearing voices that aren’t there) but they can occur in any sensory system — like seeing images or feeling touched by something that doesn’t exist.