Many patients with a primary psychiatric disorder report sleep disturbances that change across the lifespan and also vary with gender. These alterations in sleep may influence the development and course of a psychiatric disorder, and thus treatment of the psychiatric disorder can significantly improve sleep.
Conversely, when the sleep disturbance predominates, its treatment may improve the management of the mental disorder. For example, sleep disturbance is a relevant symptom when establishing a diagnosis of generalized anxiety disorder (GAD). In addition, studies report that the severity of the insomnia parallels that of the anxiety disorder.
Importantly, a one-year study that includes 8000 subjects indicates that insomnia could be a causative factor of anxiety. Similarly, GAD could also be a risk factor for the occurrence of chronic insomnia. According to all-night polysomnographic studies (i.e., sleep studies), individuals with mild to moderate GAD have more difficulty staying asleep but less difficulty falling asleep.
Strategies intended to help with sleep disturbances include adopting sleep hygiene that excludes caffeine and nicotine, limits fluid intake close to bedtime, and involves regular bedtimes and waking times.
Reference:
Monti, J. M., & Monti, D. (2000). Sleep disturbance in generalized anxiety disorder and its treatment. Sleep Med Rev, 4(3), 263-276. doi:10.1053/smrv.1999.0096