I’ve been struggling with depression, anxiety and panic attacks for about 6 years now. I have had problems with depression since I was a child, but the anxiety and panic cropped up 6 years ago.
First, I have to say that drugs are NOT necessarily the answer. They can help quite a bit, especially when things are particularly bad but they can also turn out to be a horrible physical and mental crutch that is nearly impossible to break free of. If you need them occasionally then take them of course, but they should be a 'band aid' fix. Please be very wary of any Doc that tells you that you may be on them for the rest of your life, how will you ever know if you are better if you never give your body a chance to get away from the drugs for a while???
When my panic started, I would have attacks that would literally last for hours - my 'record' was just over 8 hours. That would be 8 hours of shaking, heart pounding, sweating, confusion, jumpiness, and terror. I'm sure you know the feeling. I didn't always have anxiety when I had panic attacks, but anxitey attacks were usually followed by panic attacks.
I went into severe depression last year. I had to force feed myself and I was barely functioning - at work or at home. I ate because I knew I had to eat, not because I was hungry. I got out of bed because my parents called me every morning to make sure I was up. My sister called me every night to make sure I was home. My parents called me in the evening to make sure I was going to bed. Anxiety and panic was making me crazy at work, and I frequently had hysterical sobbing fits. I went on drugs and started up therapy again (I hadn't been to a shrink since college). The drugs lasted for 6 weeks, Zoloft helped the depression, but the anxiety was out of control while I was on it. Once I got over 'the hump' I weaned myself off of the Zoloft. I still say a good shrink is the key.
Your panic is being triggered by something. It has to be. It may be something you don't consciencely recognize. That's where a good shrink comes in. It's too bad that repressed memories have become such a 'hollywood cliche', because they are very real and can be extremely powerful. Personally, the sexual abuse I suffered as a child has caused me to repress most of my childhood, and I have learned that certian things trigger memories and those triggers also send me into a anxiety and/or panic attack - without me ever actually remembering an 'event'. It is something to think about and explore. I don't know how old you are, but if you have a definate start point for your problem then something that happened at that point in your life may be the cause. Facing things down on your own can be very difficult though, so be sure you have a trusted therapist or a good support network to help you.
For me, talking is key. I tend to be obsessive, and the more I talk about things the less I obsess about them. Things often click into place when I discuss them in depth with someone. I like talking with a therapist because I can walk away from the topic when I need to. It's hard with a friend because if they help you with the really bad stuff then you may come to associate them with the bad stuff that they help you with and they will end up being a trigger. This ruins friendships - trust me on that one.
I agree 100% with the person who said that anyone who says 'snap out of it' has NO idea what they are talking about. When your own brain is fucking you over there is no easy, fast way out.
I also agree that exercise is very important, especially long periods of running / biking / cross country skiing - anything long and sustained. I ususally obsess for a while, but after a while I settle into a rythm and focus on my body working. I also like to horseback ride, but I don't get the same sort of calming effect because I have to pay attention to the horse!
It seems you have tried all the meds out there. May I suggest you give up on them for a while? Patterns have specific repeating triggers - seasonal affectiveness disorder for instance goes with the seasons and sine seasons are not going away anytime soon, people with SAD learn to handle thier specific triggers. Perhaps your panic started as a yearly thing that was triggered by the anniversary of an event (or beginning of a series of events)? As you become accostomed to the cycle, the anticipation can cause the cycle to shorten, becoming a self fulfilling prophecy.
Just some things to think about.
(I must apologize if I have rambled, it is very late and I am on a caffine high from my drive home...)