It's a long hard battle but try to stay sober and work it out of the system- I had a similar experience with LSD when I was 18 - I can relate the anxiety attacks that you describe, they were very intense for a few months and it took a good six months for me to feel 'normal' again.
I agree with the others here, sure, weed can help some people but it can also drag the whole messy experience out so it's probably not advisable, you want to recover healthily, quickly & properly.
The question here is why? the anxiety attacks:
I reasoned it like this: What I saw during that trip was enough to make me believe that I wasn't back on planet earth. It was that intense, visual hallucinations weren't limited to "wow, that cigarette packet is mutating" but rather "what the fuck is this intense light show that's going on all around me (when my eyes were open or closed) - there was simply no escaping it and parts of my brain simply shut down (they were essentially dormant). The triggers for the anxiety attacks relate to my first comment, it's this notion that what I saw on the other side was so powerful that my brain was continuously questioning reality... for six months. Naturally, it got easier in time - but that's what I believe was going on up there in my brain.
How to deal with it? My solution was, ultimately, rather simple - Let's say for a moment that what we do indeed see is all illusion... well, there's nothing I can do to change that - so I might as well live with it. Accept this and the fascination with the "is it real? isn't it?" debate that's wizzing round like a sports car in your head will slowly subside...
I thought I was fucked for life - 15 years later I can say with my hand on my heart that nothing is wrong with me, nor do I feel that I damaged anything back then. The brain is far more complex than whatever a tab of lsd can do to you. You just need to ride it out.
One word of caution - the exact same thing happened to someone I know way back then who was around my age. - He did get help and the problem exploded to the point where he's on heavy duty meds to this day and is generally in poor mental shape. It wasn't the drugs that did this, it was the way those around him reacted to his experience - in particular, overbearing parents.
Truth is, we know so little about the brain to this day that no one is really going to fully grasp what you've been through. If you are going to make a recovery, do the research yourself and be very careful how you talk to others - most normal people won't have a clue what you've been through. Read books - In particular, read 'The Doors of Perception' - I learnt more in that book about my experience than any doctor or 'professional' could ever have taught me. Be objective, and try to find out what makes sense to you and what helps you to rationalise the experience to yourself.
[sermon over]
