To begin with, if you are taking Citalopram (Celexa) for anxiety, I recommend that you start at a low dose. 10 mg is a good dose to start with. By starting at a low dose, side effects are less apt to occur, and those that do can be less severe. After being on 10 mg for some 10-12 days, you can go up to 20 mg, which is the lowest therapeutic dose (20-40 mg is normal dose range for Citalopram).
Regarding side effects, some people have none at all, others have some mild side effects, and some more severe. Normally seem side effects with Citalopram include an actual increase in anxiety, sweating, and insomnia, to name a few. The increase in anxiety is because serotonin levels in the brain are immediately increase when starting a selective serotonin reuptake inhibitor (SSRI). Most side effects usually dissipate in about two weeks.
Anti-depressants take a lot of time to work, as they encourage the growth of new brain cells in the hippocampus region of the brain. Cells in this region can be damaged or destroyed by stress hormones such as cortisol. So just like a broken bone takes time to heal, so does your brain. Between a 3-12 weeks period, individuals will usually see degrees of improvement in there symptoms.
I am on Citalopram (Celexa), and to give you some idea, I saw a decrease in my depression and negative thoughts at about 3-4 weeks into treatment at a therapeutic dose. Anxiety started to diminish at around week 10.
By-the-way, if you do start out at 10 mg, don't consider that time as part of your treatment. 20 mg is the lowest therapeutic dose, so once you reach that 20 mg mark, consider that the start of your therapy.
Let us know if you have any other questions as time goes by in your treatment...
The very best to you, Nat!... Chuck