Insomnia is the perception of inadequate or poor-quality sleep. It can be due to problems falling asleep, early wakening, waking frequently during the night, unrefreshing sleep, or a combination of these. Contrary to some popular beliefs, insomnia is not defined by the total amount of sleep one gets or how long it takes a person to fall asleep. Individuals can vary in their need for sleep, and in the time required to fall asleep. What is a refreshing night's sleep for one person might be insomnia for another person. Insomnia may be classified by how long the symptoms are present. Temporary insomnia (transient insomnia) usually is due to situational changes, such as travel and stressful events. It lasts for less than a week or until the stressful event is resolved. Short-term insomnia lasts for one to three weeks, and long-term insomnia (chronic insomnia) continues for more than three weeks. Insomnia may also be classified as primary or secondary. Primary insomnia occurs in the absence of other medical problems, while secondary insomnia occurs as a result of a medical condition such as heart disease, arthritis, cancer, or heartburn causing wakefulness. Insomnia is more likely to occur in females, people over 60 years of age, and people who have a history of depression, however, anyone can be affected by insomnia. Short-term insomnia may also occur as a side effect of certain medications. Chronic insomnia is more serious and may be caused or worsened by a variety of mental and physical problems. Although sedative medications may be prescribed by a doctor for severe cases of insomnia, their use is controversial in management of long-term insomnia. Many treatments for insomnia are behavioral in nature; for example, identifying and reducing behaviors that worsen the insomnia or learning and practicing relaxation techniques. Insomnia can be particularly devastating because it often leads to a "vicious cycle" of daytime behaviors that worsen the condition. Persons without adequate sleep can experience tiredness, lack of energy, and concentration problems; which they may attempt to overcome by excessive caffeine intake or nicotine use. Insomniacs may be "too tired" to exercise and take afternoon naps, both of which reduce the ability to fall asleep the following night.