If it has to do with anxiety a lot of people think there having a heart stack when they're really having a panic attack, because your heart speeds up a ton and you having a lot of anxiety already which can cause paranoia. If it is a panic attack then there are lots of ways to deal with it the number one way is to try to destruct your self and to remember that your not in any danger and that it will pass. Also headaches can manifest from stress or anxiety.
You should talk to your doctor about different medications that the side effects are more tolerable.
Good luck with your headaches. I hope they get better.
There are other meds to choose from so I don't understand why she did'nt try you on something else. It's true that Celexa may have been causing your headaches. All meds come with possible side effects. Can you get back in to see her and ask about another med to try?