What is depersonalization?

Can you describe depersonalization to me, and what it feels like? I'm trying to wrap my head around the definitions I've found and whether or not they apply to things that have happened to me.

I used to have it really bad, basically you feel like you don't really exist and can't feel any emotion at all. Mine was brought on by panic attacks and made worse by psyc meds. The good news is that it will go away with time! Hope that helps.