Many many people, including many on this site, got their first panic problems while high on marijuana. It brings out things that are inside us and intensifies the experience. What you're feeling now is the memory of the bad experience, and it might be a good idea to see a therapist who specializes in anxiety to get this conditioned thinking under control. Any drug that gives you anxiety isn't necessary for you to be using, and marijuana now falls into that category for you. It's great when it's great, but no fun when it's not. That's just life.
I can relate to you,because i also smoke marijuana and suffer from depression,but i gotta say its okay,best thing it helped for me is to stay calm,nothing is gonna happen,stay calm,do not think about how you gonna die,cause it wont happen,try to smoke it alone,try different things,be in the right environment when you smoke marijuana! your'e just probablly scared of dying,and marijuana is the last thing that could kill you right now (no deaths by marijuana is recorded anywhere),start meditating,relax,im speaking from my own experience.enjoy life,important part is to remember that you gotta stay busy with something so you wont think about being depressed and anxious and it will go away...stay positive:) remember,life is good:) get yourself some positivity in your life.that's what helped me,hope it helps,cheers!