Psychotic thoughts can be associated with bipolar depression. Here's an explanation of bipolar depression with psychosis, plus examples.
I certainly don't want to leave depression out of the discussion! Mild to moderate psychosis- the kind that resides on the gray area and just on the other side of the continuum is common with depression. I've had this type of psychosis, on and off, for my entire adult life ever since seeing myself get killed by a bus after breaking up with my first boyfriend at age 19. Paranoid ideas and possibly delusions, such as thinking people are talking about you behind your back, are quite common with depression as well. Full-blown psychosis can be seen with very severe depression.
Depression can lead to such destructive, mean, intrusive, scary and ultimately dangerous thoughts that it's easy to confuse these thoughts with psychosis. A person with depression can think and believe the following things:
I wish I were dead and buried under the ground and trucks would run over my grave every day.
Life is a waste. I'm a waste. I'm the lowest, most disgusting, nasty, unloved creature on the earth. I'm putrid with my disgusting thoughts and face.
If I took that knife and stuck it in my heart, I would not be missed and the world would be a better place.
But this is not psychosis. These are feelings and thoughts fueled by profound unhappiness and self-loathing and disgust. They are scary and outside of the norm, but they are mood congruent. In other words, the person really does feel this bad and their thoughts are a reflection of their mood.
When a person in a depression moodswing moves into psychosis, the thoughts are similar to those above, but they become bizarre:
I am dead. My body has rotted and I am the only one who can see this. I must cut out the dead parts of my body so it doesn't spread. I have the plague.
There is a demon inside of me that will kill my family if I let him out. I am never going to leave my room so that no one will get killed. The demon talks to me when the lights are out and there is no one to protect me.
Interestingly, the above thoughts are psychotic, but they are easy to follow. board certified neuropsychologist, John Preston, Psy.D. explains, "You can have severe psychotic symptoms with depression, but you don't have the gross disorganization of thinking you can see with severe manic or dysphoric manic psychosis. Despite their very odd and unreasonable thoughts and actions, people with psychotic depression usually have logical sentence structure and can answer questions in a realistic way that makes grammatical sense. Depressed people are reclusive and there are behavioral changes, but they are not bizarre."