For many years, insomnia was considered to be primarily a symptom of another illness, writes Wallace Mendelson in The Science of Sleep. During his 40-plus years as a sleep researcher, Mendelson has seen many views evolve, and this is one of them. In addition to being the result of some other underlying condition, insomnia may also be a free-standing disorder in its own right, which means it needs its own treatment. In fact, researchers have found that treating sleep disturbances can decrease the symptoms of other illnesses. Interesting new studies make this an exciting time for researchers and insomniacs alike.
Mendelson, Wallace B. The Science of Sleep: What It Is, How It Works, And Why It Matters. U of Chicago P, 2017, p. 149.