Getting technical....

...and citing sources. This comes from Dr. Heather Ashton at www.benzo.org.uk/ and if you go to the website and look at the photo of the lady, you will be assured that she knows her stuff. (I did a slight bit of editing to shorten the passage.)

(1) Dosage tapering. There is absolutely no doubt that anyone withdrawing from long-term benzodiazepines must reduce the dosage slowly. Abrupt or over-rapid withdrawal can give rise to severe symptoms and may increase the risk of protracted withdrawal symptoms. Slow withdrawal means tapering dosage gradually, usually over a period of some months. The aim is to obtain a smooth, steady and slow decline in blood and tissue concentrations of benzodiazepines so that the natural systems in the brain can recover their normal state.

Long-term benzodiazepines take over many of the functions of the body's natural tranquilliser system, mediated by the neurotransmitter GABA. As a result, GABA receptors in the brain reduce in numbers and GABA function decreases. Sudden withdrawal from benzodiazepines leaves the brain in a state of GABA-underactivity, resulting in hyperexcitability of the nervous system. This hyperexcitability is the root cause of most of the withdrawal symptoms. However, a sufficiently slow, and smooth, departure of benzodiazepines from the body permits the natural systems to regain control of the functions which have been damped down by their presence. There is scientific evidence that reinstatement of brain function takes a long time. Recovery after long-term benzodiazepine use is not unlike the gradual recuperation of the body after a major surgical operation. Healing, of body or mind, is a slow process.
The precise rate of withdrawal is an individual matter. It depends on many factors including the dose and type of benzodiazepine used, duration of use, personality, lifestyle, previous experience, specific vulnerabilities, and the (perhaps genetically determined) speed of your recovery systems. Usually the best judge is you, yourself; you must be in control and must proceed at the pace that is comfortable for you. Actually, the rate of withdrawal, as long as it is slow enough, is not critical. Whether it takes 6 months, 12 months or 18 months is of little significance if you have taken benzodiazepines for a matter of years.

So thank you Dr. Ashton for being informative, unarrogant and humane. In my experience, those characteristics are rare in a psychiatrist.