A lot of times meds can have paradoxical start-up anxiety/depression. It's possible that sometimes the brain reacts against the unusual surge of serotonin by depleting it instead. AD's take a long time to finally work for you, which has a lot to do with long term changes in your brain.
(maybe, you know, as far as we know)

It's hard to say if the panic is from the med or your usual anxiety. Consider that you've already been experiencing panic attacks without the medication. It's also easy to get the idea "in your head" that the meds are screwing with your mind, gonna mess you up, make you worse, etc. And with the horrible spiraling effect that comes with anxiety, a little nudge of an effect you recognize from the meds could easily cause someone to think it's actually more than that.

A lot of people take ADs and ultimately feel worse. Yet a lot of people feel initially worse and then get much, much better. Start-up anxiety doesn't mean that the medication couldn't be ultimately helpful.