Insomnia was a medical symptom characterized by an inability to sleep.
Trip Tucker began suffering from insomnia after the Xindi attack on Earth. (ENT: "The Xindi")
When Geordi La Forge was brainwashed by Romulans in 2367 he also suffered from insomnia. He came to sickbay and Doctor Beverly Crusher gave him an somnetic inducer to help him sleep. (TNG: "The Mind's Eye")
In 2369, Julian Bashir claimed a Bajoran officer was suffering from hormonal chronic insomnia. (DS9: "Dramatis Personae")
After encountering the Dream species in 2374, many USS Voyager crewmembers began suffering from acute insomnia. (VOY: "Waking Moments")
Julian Bashir described the Kal'Hyah ceremony as being a "feast of insomnia and discomfort". (DS9: "You Are Cordially Invited")