Just because you are not "feeling" anxious doesn't mean the adrenaline, the subconscious thoughts, and the fears aren't still there. If you suffer from an anxiety disorder it preoccupies your mind. The fears persist because they refuse to leave your mind. They seemingly re-emerge, but in reality, you do think about them, and you will have a fear at the back of your mind even without thinking about it, contributing to pretty much any physical symptom under the sun. They never truly leave your mind until you learn to handle and view the fear more positively. Someone who has had bad anxiety for a longer period of time cannot possibly feel better instantly. It takes time, a lot of time, for excess adrenaline, increased adrenal function, stress hormones, to leave your system.
Anxiety is a natural fight or flight response that faults because there is no real threat, only perceived threat. You requiring help, worrying about these symptoms, proves to me at least that while you do have a good day here and there, that the anxiety itself is being persistent.
I can't tell you how to get rid of anxiety because it is an inborn natural fight or flight response in every single living human being, and in many other animals. It's self preservation. I can recommend that you look into mindfulness, actually practice it, and also try different techniques like online or in person cognitive behavioral therapy.
In-person cognitive behavioral therapy can be expensive (I've done about 12 sessions of it and it costs roughly 200 dollars an hour for me), so if you're not able to pay for that, then try this site list:
Cognitive behavioral therapy:http://en.wikipedia.org/wiki/Cognitive_behavioral_therapyhttp://psychology.about.com/od/psychotherapy/a/cbt.htmhttp://www.nacbt.org/
Also look into When Panic Attacks
and Feeling Good
by Dr. David Burns. Two good books I've bought to help me combat my own anxiety and my depressive thoughts and hopelessness associated with these feelings.