That sounds awful, sorry. My advice would be to start out slowly. Do you live near any countryside? Maybe try to go with a friend and just walk about outside and gradually progress until you feel more comfortable in big places. You see, for me personally, and I know this might not apply to you, I feel more relaxed and generally happy if I am in a massive, crowded place. It might be to do with the anonymity of a big city partly. Maybe it's a question of the way you think about it? A mind over matter type situation. I don't really know much about panic attacks!
What sort of things do you fear?
(Also, never do LSD!)