Psychosis (imo) is a severe reaction to distress. People are not psychotic all the time, mental health naturally goes up and down in our lives. Psychosis can be part of many different mental health issues, in your case it is part of the depression, it's not unusual. It would be interesting for you to keep a diary of the times whan you feel more distressed and see if there are any triggers and you can also work with your therapist on reducing stress and this will help the psychosis too.