One study has indicated that the incidence of sexual and physical abuse is higher in female patients with FM than in the general population. This could indicate that post-traumatic stress syndrome may play a role in the development of this disorder in some patients. Post-traumatic stress disorder (PTSD) is an anxiety disorder that is a reaction to a specific traumatic event. Symptoms of this condition, which can occur for years after the traumatic event include emotional withdrawal, hopelessness, irritability, mood swings, sleep problems, inability to concentrate, and an excessive startle response to noise. There is some evidence that PTSD actually results in changes in the brain, possibly from long-term overexposure to stress hormones.