http://www.thelancet.com/journals/lanpsy/article/PIIS2215-0366(17)30328-0/fulltext?elsca1=tlpr [thelancet.com]
In the largest randomized control trial for mental health, researchers discovered a link between between insomnia and to paranoia and hallucinations. Successful treatment of insomnia cut paranoia and hallucinations by around half. While the researchers don't extend similar links as existing outside the studied population, the correlation is quite clear and strong that treatment of insomnia could lead to improvements in other mental health symptoms in other populations.