Insomnia is defined as a persistent difficulty with sleep despite having the opportunity to sleep, leading to daytime impairment, and can be classified into transient, short-term, and chronic forms. Chronic insomnia may arise from various medical, psychological, or substance-use disorders, while primary insomnia is not linked to any health problems. Treatment options include relaxation and cognitive behavioral therapy, as well as medications like triazolam, temazepam, and flurazepam.