Insomnia was a medical symptom characterized by an inability to sleep. One who suffered lapses of memory and ability after lack of sleep was said to be "punchy". (ENT: "Anomaly (ENT)")
Trip Tucker began suffering from insomnia after the Xindi attack on Earth, which caused the death of his sister Elizabeth. (ENT: "The Xindi", "Extinction")
Captain Jean-Luc Picard sometimes experienced insomnia and when he did, he would try to perfect his aunt Adele's recipe for a steamed milk toddy with nutmeg. (TNG: "Cause And Effect")
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 Aliens 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")
In 2375, when Valerie Archer, a member of Species 8472, took part in a simulation of being Human, she experienced sleep for the first time and with it, conditions such as insomnia. Commander Chakotay asked her if she was looking forward to returning to fluidic space, and she expressed pleasure at the thought of getting out of Human form. "No more insomnia," commented Chakotay, and she replied that she would no longer be sleeping at all. (VOY: "In the Flesh")