I am not sure what 'mclizie' is. Is this a medication? If so, I don't know of it or if you can mix it with Celexa...I would check with your doctor or pharmacist. There is also a website that you can look at for possible drug interactions.
http://www.healthline.com/druginteractions
As far as the pain in the head, it could just be caused by tension. Improper breathing can cause a whole list of symptoms because if your blood PH is thrown off (imbalance of O2/Co2) it is then being circulated to all systems and parts of your body, affecting how you feel everywhere. That is why breathing exercises are key in anxiety/panic relief!
S.C.