Research identifies three possible root causes of sleep problems. They can be organic and arise from endogenous abnormalities related to sleep-wake mechanisms. Alternatively, they can be induced by interaction with a specific substance or medication, or they can be the result of a medical condition. Lastly and more significantly, sleep problems could arise from a concurrent mental health disorder.
In fact, there is evidence that the presence of a mental health disorder is a strong predictor for later sleep problems. Previous findings highlight the role of internalizing disorders such as anxiety and depression in the emergence of sleep disturbances. Indeed, good sleep is conceptualized as requiring a sense of safety and security, but with the presence of a mental disorder, that sense of comfort is shaken. For example, studies show that children who tend to be easily upset and touchy are more likely to have sleep problems,
The research linking mental health disorders and sleep disturbances lists specifically depression, generalized anxiety disorder and separation anxiety disorders as disorders typically exhibiting sleep problems among the core symptoms. Stronger support for this link comes from reports that depression and anxiety are strong predictors of later insomnia. In other words, having one of those conditions increases the likelihood of developing insomnia later on.
More interestingly, there is also strong support for a reverse relationship between sleep problems and mental health disorder for children in which the presence of sleep problems acts as a high risk factor for later development of a mental health disorder. Particularly, there is evidence that sleep problems in children predict later psychiatric disorders specifically from a cluster of mental illness that includes generalized anxiety disorder (GAD).
Admittedly, one core characteristic of GAD is irritability, which may point to the individual’s inability to regulate negative emotions and thus achieve a sense of peace that is necessary for the promotion of sleep.
Furthermore, looking at individual sleep symptoms reveals that difficulty falling asleep may be one of the strongest factors in the relationship between sleep difficulties and GAD in both directions. Thence, successful treatment of sleep problems, including difficulty falling asleep, could help reduce the risk for GAD.
Reference:
Shanahan L, Copeland WE, Angold A, Bondy CL, Costello EJ. Sleep problems predict and are predicted by generalized anxiety/depression and oppositional defiant disorder. J Am Acad Child Adolesc Psychiatry. 2014 May;53(5):550-8. doi: 10.1016/j.jaac.2013.12.029. Epub 2014 Feb 20. PMID: 24745954; PMCID: PMC4144678.