Stress-related disorders like the ones you named are caused by abnormalities in Gamma-amino butyric acid (GABA) functioning, a neurotransmitter that inhibits action potentials, anxiety, and intoxication. Lower levels of GABA also can lead to Epileptic seizures. Therefore, Benzodiazepines drugs like Valium can reduce symptoms of anxiety, insomnia, and other stress-related disorders.