I haven't had this reaction with xanax but with lorazepam which is another short acting benzo. Short acting benzos are often prescribed for short term use or as needed. If you take it as needed and that turns into several times a day and you miss taking a dose at a time that you would normally take it, this rebound anxiety can rear it's ugly head. This is not a hard and fast rule, but it certainly can be a problem for many people. If you find that you are needing to take xanax more frequently possibly because of the rebound effect, you might consider talking to you doctor and setting up a schedule for taking this medication at equal intervals or you might consider going to a long acting benzo that you only need to take two to three times a day. The longer acting benzos stay in the system longer therefore you don't have the peaks and valleys of anxiety. You just have more of a steady state of calm. The long acting benzos (klonopin and valium to name the two most common) can be prescribe as needed but for those who have ongoing GAD or frequent panic attacks, there are some who benefit from taking them on a daily basis because there is no rebound effect.
Rebound anxiety is no fun and in my opinion, if you continue to have this problem, it might be worth a trip to the doctor to discuss what he would recommend to alleviate this problem. I hope this has been of some help to you.