Mom was prescribed celexa for anxiety but also given xanax (alprazolam) to take only when she feels severe anxiety coming on. does this seem reasonable?

Yes: Not unusual when treating anxiety to take a long-acting medication like Celexa and also a short-acting medication like Xanax (alprazolam) to use "as needed" for occasional severe anxiety attacks.

Yes: This combination can be very safe and effective in helping your mother feel better and have a better quality of life. Side effects can occur and may include drowsiness or GI related symptoms. There is a risk of addiction with Xanax (alprazolam) and it's use should be limited. Your mother and her doctor need to discuss this. Alcohol should be avoided. Psychotherapy with a trained therapist may also help.