I think amanda pretty much summed it up.
Psychosis and dissociation are 2 different distortions of reality.

Though dissociation is still connected to reality, you feel disconnected. I have experienced this many times. Especially going through a trauma.
Example from my experience. When I was suffering an acute distress from a trauma. Going into the grocery store was hard. It felt like everything was far away from me, yet it was closing in on me with a lot of pressure. I was extremely over whelmed and had to leave the store. It feels like you are there but separated in another dimension, not in place where you are standing, but you feel it in your mind. Everything that is familiar is unfamiliar, but yet you know it.
with dissociation your not hallucinating or in some delusion. For example your not seeing or hearing things that are not there.

With Psychosis it includes hallucinations, delusions, speech that consist of talking about one thing and then another. Though it includes that of switching from one subject to another. We all usually do that when we have a lot going on, trying to squeeze it into a short period of time. This is talking about random, completely unrelated topics. EX. If your talking to someone with psychosis you may be talking about the store that burned down last week, and then they will say something random, unconnected. (not that of talking of a different subject on the list of thought) but will suddenly say something like, " Abraham Lincoln was shot." In the middle of no where. People often get this confused when looking up things about psychosis and it is poorly expressed. Because it will say changes topic jumping from one subject to another.
Many people do that often, but this is completely different and disconnected to reality of conversation.
Though many people,I think, have delusional beliefs. This is something extreme. Many people stay convicted on beliefs many know are not real and if you try to prove it to them, they still stay on their belief. The DSM say if you carry a beliefs despite what everyone else believes. This is very vague, and not detailed enough. Delusional beliefs are not clearly defined and actually very shaky in explanation that is justifiable in the DSM.

A real delusional belief that is psychotic would be. Someone believing that their child is on a commercial on TV. and that is their child. Its not really a hallucination. They really did not see their child on TV. They just believe that is there child.

Fear of things that are not there. This does not include what would give someone an idea to fear. Though there may be nothing there just based on false perceptions that are common, or past experiences.
This would be based on random fears with nothing to give relation for that fear. For example. You may be a random housewife and you think the pope is coming after you to kill you, or you think an innocent bi-standard without reason or anything indicating it, is going to take your child.
This is paranoia. This would exclude someone making a gesture or acting out of the ordinary to give you that idea that it could be possible.