Is it true when starting prozac (fluoxetine) that anxiety/depression can get worse before getting better?

Yes: Everybody reacts differently to the ssri class. If you trust your doctor and agree with their treatment plan then i feel this is a safe medication for most people when properly diagnosed.

Brain chemistry: Very simply there are three basic chemical messengers in the brian. Dopamine ( which controls the motor aspects of the body ), noreepinephrine, ( which turbocharges, or eat or be eaten ), serotonin, ( which allows you to sort out, select, and then by staying calm, allow you to problem solve ). Durig times of stress you use up serotonin, then you use norepinephrine. In healing can get worse.

Yes: Unfortunately, it usually takes 2+ weeks for the good effects of antidepressants to start, while side-effects can happen right away. Prozac (fluoxetine) is a relatively activating or stimulating antidepressant. It can worsen anxiety, especially at first. (in fact, if anxiety was a major problem, i might choose a different ssri in the first place.) the prescribing doc should help with any side effects.