Difference between Depersonalization and Psychosis 

Can someone elaborate on this?  It seems that the overall description of these two conditions are very similar (as with many other disorders or conditions).  I know that there are some obvious differences but any big ones?  I'm mainly looking for differences in symptoms and description but anything is fine.  Causes are fairly similar and some other things.  There seems to be enough differences in the two conditions to constitute a seperate listing in the DSM but just looking for a bit more.