A shared psychotic disorder is a rare type of mental illness in which a healthy person starts to take on the delusions of someone who has a psychotic disorder such as schizophrenia. For example, let’s say your spouse has a psychotic disorder and, as part of that illness, believes aliens are spying on him or her. If you have a shared psychotic disorder, you’ll start to believe in the spying aliens. But apart from that, your thoughts and behavior are normal.