Some people do have real chemical imbalances.
I did for a while. The reason I was on paxil was for physical symptoms (gastrointestinal symptoms, IE. Crappy Pants) and it did work, becasue serotonin is used to filter the messages all over your body. Not jsut the brain. The problem is that reducing your usage of SSRIs is harder than they want you to think. Your body has to get used to producing more serotonin.
The only negative effects of SSRIs (other than the cost) is that after 10+ years of steady use your body will start to think that certain nerves in your brain are damaged becasue the excess of serotonin will casue them to fire more often. The body kills off nerves that are "out of order". I have not been on paxil for longer than 6 or 7 months and it cured my physical symptoms so I am getting off it, But if I had cronic anxiety or panic I'm almost certain I would stay on this or another ssri becasue they do work.
Warning:
This animation may trigger anxiety attacks.