Individuals vary normally in their need for, and their satisfaction with, sleep. Insomnia may cause problems during the day, such as tiredness, a lack of energy, difficulty concentrating, and irritability. Insomnia lasting from a single night to a few weeks is referred to as transient. If episodes of transient insomnia occur from time to time, the insomnia is said to be intermittent.
Insomnia is considered to be chronic if it occurs on most nights and lasts a month or more.
Certain conditions seem to make individuals more likely to experience insomnia. There are many causes of insomnia. One of the most common causes of chronic insomnia is depression. Other underlying causes include arthritis, kidney disease, heart failure, asthma, sleep apnea, narcolepsy, restless legs syndrome, Parkinson's disease, and hyperthyroidism. These behaviors may prolong existing insomnia, and they can also be responsible for causing the sleeping problem in the first place.