Why do i feel trapped?

Hi i am 17. for some reason i started feeling like i am trapped on earth... after one panic attack I had 2 months ago.. so far it keeps getting better and its not on my ind as much, but it's still there... i don't panic no more or get anxious i just get very very upset.. until it's gone.. so anyone have an explanation for me? is it chemical inbalance, and will it go away? this happens more at nights, then days.. because 2 months ago i suffered a panic attack when i went to bed... thinking of the world and me, and this happened? never had this on my mind before, so wut u think?