With. Dellusional disorder the person believes things that are not true; perhaps they see themselves as extremely important and influential with connections to powerful people, or perhaps they believe people are out to get them out of jealousy or spite, or- in extreme cases, perhaps even a close friend or family member has actually been replaced with a spy, etc. The thing is, they are not “lying”, they are truly convinced of these things.
It is important to note that a delusion is a belief; thinking that something is true even if it has zero basis in reality.
This is different from a hallucination- which is where a person’s brain tricks them into seeing and or hearing things that are not there. (The demonic voices in their head laughing that the CIA has their whole house bugged).
Dissociative disorders are different. But a strong characteristic is lack of awareness/memory of specific events/behaviors.
For example, with dissociative fugue; Johnny is working at a factory and is being careless and is about to be maimed by a piece of machinery- the next thing Johnny knows, he is on the other side of town, unharmed, but has no idea how he got there. The trauma of the situation caused Johnny’s conciousness/ego to retreat and go into sleep mode while his body ran on auto pilot and he escaped the traumatic situation. Once his body was at a safe enough distance away, his Ego (that is your sense of self) woke up again but has no memory of how they got there.
Or Dissociative Personality Disorder (once upon a time was called Multiple Personality Disorder) the individual is not consciously aware that they have another “person” in their body (Like Dr. Jekhl and Mr. Hyde but no murder) it is a coping mechanism for trauma- their main personality is unable to cope or endure certain stressful situations, so their brain essentially “turns off” their persona, and invents a new “person” to temporarily take their place- this new identity often has different personality traits and quirks, different memories, even different likes and dislikes, and may even be a different age or gender than the original personality. But the different personalities do not share memories. And the patient does not realize that they have another personality that “takes over” all they know is that they have gaps in their memory and often “wake up” not knowing how they got there or what they were doing beforehand.
Basically, with Delusions, what they believe is true is different from reality.
With Dissociation, reality completely turns off as your brain reboots and by the time you are back to your senses you have no idea what happened while you were “out of it”.