I know what you mean, it can come in waves.

Knowing what your triggers are is good but sometimes anything appears to trigger it.

Anxiety is a fear response and that fight/flight response can be useful but not all the time!

Several things you can do to help-

Self-talk, reassure yourself that everything is ok, your safe etc........

Step outside and really concentrate on everything that is around you. The trees, the plants, the feeling of the wind etc.........

Practice slowing your breathing down, if feeling really bad cup your hands over your face and breath steadily for at least 10 minutes.

Buy a relaxation tape/CD and practice at least once a day. Or learn how to do meditation.

Distractions- playing computor games or listening to music to take your mind off the worry.

Hope some of these tips help.