The following paragraghs from the Ashton Manual..
Mechanisms of withdrawal reactions. Drug withdrawal reactions in general tend to consist of a mirror image of the drugs' initial effects. In the case of benzodiazepines, sudden cessation after chronic use may result in dreamless sleep being replaced by insomnia and nightmares; muscle relaxation by increased tension and muscle spasms; tranquillity by anxiety and panic; anticonvulsant effects by epileptic seizures. These reactions are caused by the abrupt exposure of adaptations that have occurred in the nervous system in response to the chronic presence of the drug. Rapid removal of the drug opens the floodgates, resulting in rebound overactivity of all the systems which have been damped down by the benzodiazepine and are now no longer opposed. Nearly all the excitatory mechanisms in the nervous system go into overdrive and, until new adaptations to the drug-free state develop, the brain and peripheral nervous system are in a hyperexcitable state, and extremely vulnerable to stress.
Acute withdrawal symptoms. The most prominent effect of benzodiazepines is an anti-anxiety effect - that is why they were developed as tranquillisers. As a consequence, nearly all the acute symptoms of withdrawal are those of anxiety. They have been described in anxiety states in people who have never touched a benzodiazepine and were recognised as psychological and physical symptoms of anxiety long before benzodiazepines were discovered. However, certain symptom clusters are particularly characteristic of benzodiazepine withdrawal. These include hypersensitivity to sensory stimuli (sound, light, touch, taste and smell) and perceptual distortions (for example sensation of the floor undulating, feeling of motion, impressions of walls or floors tilting, sensation of walking on cotton wool). There also appears to be a higher incidence than usually seen in anxiety states of depersonalisation, feelings of unreality, and tingling and numbness. Visual hallucinations, distortion of the body image ("my head feels like a football/balloon"), feelings of insects crawling on the skin, muscle twitching and weight loss are not uncommon in benzodiazepine withdrawal but unusual in anxiety states