These symptoms are related to the way we perceive ourselves.
Derealization is the feeling that you yourself and all around you is unreal, like a dream, like everything you see through fog, or a filter. These symptoms can be very disturbing.
Depersonalization is the feeling that you are out of the body and like you look at it from another angle. It is noticed that people experience panic attacks and depersonalization and derealisation. Some first experience depersonalization, which then causes panic and derealisation.