I use Xanax very very rarely and usually less than half of the .5mg dose. With my history it was questionable if I could do this, but it turned out that I could. I knew that if I took it all the time I would build up a tolerance, so I didn't. I was fortunate. Sometimes just knowing I had it available was enough to get me through.

Did you see this thread on breathing exercises? They are so helpful to get rid of that rock in the chest feeling, and they are free and can be done whenever they are needed. It takes just a few times practicing, and then the skills are all yours
Here is a link to that thread:
http://forums.psychcentral.com/showthread.php?t=148389

Talk therapy is so helpful too.