The simple answer is that yes, anxiety can linger in the system for a very long time.
You have to remember that your body has to be ramped up enough to exhibit symptoms of stress and anxiety. This is an extremely heightened state of being, and you didn't to that state overnight. So it stands to reason that, even with consistently-applied stress reduction techniques, it's still going to take your nervous system a long time to come back down to pre-symptomatic levels. And until it does, your body CAN AND WILL exhibit symptoms of stress anxiety how and whenever it wants, even if you don't particularly "feel" anxious.
What does "a long time" mean? That's different for everyone, and it really depends on how we react to the symptoms we feel that will determine how long our anxiety sticks around. For me, I had very "heightened" anxiety (panic attacks and the like) for about eight months or so, but even after I calmed down eventually, bodily symptoms stuck around for another five or six months. Even now, several years since the worst of it, I notice that it takes less stress for me to feel symptomatic. However, I realize now that what I'm feeling IS just stress-based and nothing dangerous.
In my opinion, and my own experience, it's of utmost importance to get yourself psychologically to the point where, when these symptoms happen, you DON'T react negatively or fearfully. A lot of therapists call this "floating" or "mindfulness." Maybe you're sitting on the couch, feeling fine, and suddenly your heart starts racing (for instance). You can react either one of two ways. You can notice it and freak out—maybe start taking your pulse, or googling "fast heart rate," or posting on here for reassurance, or (worst of all) assuming something's really "wrong" and running to the ER. OR, you can calmly observe that your heart is racing and let it, knowing that it's just stress hormones in the body and that you're not in any danger. To react fearfully will keep the cycle going—because all you're really doing is increasing the stress in your body—while reacting non-fearfully will EVENTUALLY lessen your stress hormones to where your body is no longer symptomatic.
It's hard when you notice that you do have a "good" day, or a day when you're not symptomatic, and then maybe those sensations come back and you think, "oh crap I thought I was through with this." Good days, bad days—these will come and go. The key is A) acceptance of anxiety as your diagnosis, and B) understanding that recovery is neither a particularly quick nor linear process. When the buzzing and vibrations come, let them. Tell yourself it's JUST anxiety, and that by remaining calm, you're giving your body a chance to relax and heal. Gradually, you'll find that your episodes will grow farther apart and become less severe.
This post: http://www.anxietyzone.com/index.php/topic,58186.0.html
links to a very well written HA module that explains more the science about this.