I have definitely heard of the withdrawal symptoms, but for me, the medication works so incredibly well that I decided it was worth the risk. I know from personal experience that ADs affect everyone differently. I have tried a few and they all had different side effects for me. Effexor has helped the most. I have been on it for about 2 months or so. At about six weeks I began to see a marked difference in my anxiety and IBS symptoms.
As to the recurrence of panic attacks, I suppose that all depends on what is causing them in the first place (i.e. chemical imbalance, stress, anxiety, etc).
The doctors I have been to believe that my anxiety is caused by a serotonin imbalance, which explains why Effexor works for me since it works on your serotonin levels. I know when I go off the ADs my anxiety always returns. This probably set off my initial panic attack years ago and that attack prompted me to obsess about another attack, thus, causing more panic attacks and making my IBS worse.
After my first round of ADs (Zoloft) and with some cognitive behavioral therapy and yoga, I learned to recognize when I was getting that "panicky" feeling and control myself. I have not had a full-on panic attack for about 5 years now. Even when I went off the meds.
I think if you are concerned about your anxiety and panic attacks you should definitely see your doctor. If Effexor didn't work for you, then try something else. However, I know that it has been improved (according to my doctor) from its older version. An AD may be the thing you need!
Let me know if I can answer anything else for you! ((Hugs)) Hope you feel better soon!