Preface: I am not a doctor, but I am a therapist...
Why does your doctor think it is anxiety? Anxiety doesn't cause a broken back, chest infection,or COPD.
Yes, symptoms of GAD (generalized anxiety disorder) can include sleep disorders (both not sleeping or too much sleeping), irritability, heart palpitations, feeling "off." But, it's also accompanied by a feeling of worry on most days than not, for at least six months. Do you feel worried? Thinking or ruminating on the same thing over and over? Any panic attacks?
Recovering from illness and injury can cause depression and anxiety. Counseling, mindfulness meditation, and moderate exercise are the first lines of treatment for anxiety and depression... particularly when chronic illness is involved.
Citalopram has side effects. You need to call your doctor right away and report how you feel; please don't try to change the dose without medical advice. It is used mostly to treat depression, but is prescribed, somewhat off-label for anxiety. I am not opposed to medication at all, but it's a little unusual to be prescribed an SSRI without a recommendation for therapy and other non-medical treatments.