Ren I suffer from panic attacks too, specially if I am in a new area and don't know where the toilets are, or if its too crowded..mine can last from anywhere from 5 minutes to 45 minutes (worse on planes!!)
I use the breathing techniques that a friend told me about.. breathe in for one, two three four,.. and then breathe out.. one.. two ... three .. four.
And for a natural herb thing - I use Rescue Remedy spray.