Depersonalization is defined as feeling unreal and detached from your body’s thoughts, sensation and actions. It’s like you’re observing yourself and your thoughts. Things don’t seem real.
Derealization is defined as feeling unreal and detached but this time with respect to your surroundings and environment. In this case, you aren’t looking at yourself or feeling out of body, but your environment doesn’t seem real. It might seem like you’re in a dream.
Depersonalization derealization disorder tends to start in adolescence or early adulthood. It would be very unusual for someone to have the disorder for the first time in their 40’s or 50’s unless the symptoms are the result of something else.
There are other things that can cause derealization or depersonalization where it is not a separate disorder. You can have these symptoms that come and go. Some things that can cause this are drug use. Marijuana is a big one. This can also happen with medications such as antidepressants.