[header] How to diagnose a brief psychotic disorder [title] Notice the presence of delusions. [step] Delusions refer to strange ideas or beliefs that a person expresses. They are often unrealistic and illogical. 
Other people may find the ideas or beliefs to be strange and unbelievable. [substeps] Types of delusions can include thinking that something that something is happening when it is not really happening, such as that your significant other is cheating on you when he or she is not.