Fear is a common symptom of anxiety and depression. Almost always one of the predominate ones. Our nervous systems are 'out of wack' and we feel unstable as a result. Few people really appreciate their nervous system and it's complexities.
You should discuss this symptom with your doctor and see what he can do.
Since you have been on the Celexa for so long, it is probably no longer working for you. This is normal as our bodies build up a tolerance to it, and we need to switch medications.
Call your prescribing doctor and let him know how you are feeling, he will know what to do. Take care!