I understand. Mine happen the same way. Don't have any for a while, then all the sudden sitting at work, or standing in line at the store and it hits out of know where.
I would like to know how to get past the anxiety of waiting for the next one to happen.
And sometimes its not a full blown panic attack, but just the anxiety...anxious unsettled feeling of when is the shoe going to drop.
Hopefully someone can help us both find the answer!