I would say that your body is immune to it. I was on that same med and i started getting alot of panic attacks! When you switch they have to weeen you off the citalopram slowley and then you are stuck a week with out taking anything! I went from citalopram to effexer and i was sooooo scared to switch also. I just told myself that i have to do this otherwise its only going to get worse and i was on the pills for 6 years! When you switch it is important to NOT read any of the side effects because you are going to freak yourself out! I refuse to read the side effects because i know that im going to think that i have every single one that is written down. Let me know if you need anything or have any questions! Good luck hope u feel better :)
i was on celexa for 7 years worked well then stopped helping had to switch to zoloft,,
Sorry you are going through such a hard time right now. I know that sometimes when you are taking a medication for a long period of time it can become less effective and you might have to change your medication or change your dosage. I don't know if this would be the case for you but that is something you should talk to your dr about.
In the meantime try keeping a journal. It might help you to get some of what you are feeling inside out and might help calm you down. Also make sure you are eating right, getting enough sleep and exercising.
Are you seeing a psychatrist? It might not be a bad idea to see one if you aren't currenlty doing so. A psychatrist would work with you to get to the bottom of your anxiety as well as figure out the best medication and dosage that will help you. You can overcome anxiety but in order to do that you have to deal with what is causing it.
Good luck. I hope you feel better soon.