Insomnia is the most common of all sleep complaints. Almost everyone has occasional sleepless nights, perhaps due to stress, heartburn or drinking too much caffeine or alcohol. Insomnia is a lack of sleep that occurs on a regular or frequent basis, often for no apparent reason.

How much sleep is enough varies. Although 7 1/2 hours of sleep is about average, some people do fine on 4 or 5 hours of sleep. Other people need 9 or 10 hours a night.

Inability to get a good night's sleep can affect not only your energy level and mood but your health as well because sleep helps bolster your immune system. Fatigue, at any age, leads to diminished mental alertness and concentration. Lack of sleep is linked to accidents both on the road and on the job.

• Fatigue

About one out of three people have insomnia sometime in their life. Sleeplessness may be temporary or chronic. You don't necessarily have to live with sleepless nights. Some simple changes in your daily routine and habits may result in better sleep.

Signs and symptoms

Signs and symptoms of insomnia may include:

• Inability to sleep enough at night

• Difficulty falling asleep at night

• Waking up during the night

• Waking up too early

• Awakening not restored, even after a full night's sleep

• Daytime fatigue or sleepiness

• Daytime irritability

• Anxiety

• Fatigue

Causes

Common causes of insomnia include:

• Stress. Concerns about work, school, health or family keep your mind too active and unable to relax for sleep. Excessive boredom, such as after retirement or during a long illness, also can create stress and keep you awake.

• Anxiety. Everyday anxieties as well as severe anxiety disorders may keep your mind too alert to fall asleep.

• Depression. You may either sleep too much or have trouble sleeping if you're depressed. This may be due to chemical imbalances in your brain or because worries that accompany depression may keep you from relaxing enough to fall asleep when you want to.

• Stimulants. Prescription drugs, including some antidepressant, high blood pressure and steroid medications, can interfere with sleep. Many over-the-counter (OTC) medications, including some pain medication combinations, decongestants and weight-loss products, contain caffeine and other stimulants. Antihistamines may initially make you groggy, but they can worsen urinary problems, causing you to get up more during the night.

• Change in your environment or work schedule. Travel or working a late or early shift can disrupt your body's circadian rhythms, making you unable to get to sleep when you want to. The word circadian comes from two Latin words: circa for "about" and dia for "day." Your circadian rhythms act as internal clocks, guiding such things as your wake-sleep cycle, metabolism and body temperature.

• Long-term use of sleep medications. Doctors generally recommend using sleeping pills for only up to 4 weeks, or until you notice benefits from self-help measures. If you need sleep medications for longer, take them no more than two to four times a week, so they don't become habit-forming. Sleeping pills often become less effective over time. If you're taking sleeping pills every evening and they help, keep taking them. If they lose their effectiveness, you might sleep better by slowly withdrawing from them.

• Medical conditions that cause pain. These include arthritis, fibromyalgia and neuropathies, among other conditions. Making sure that your medical conditions are well treated may help with your insomnia.

• Behavioral insomnia. This may occur when you worry excessively about not being able to sleep well and try too hard to fall asleep. Most people with this condition sleep better when they're away from their usual sleep environment or when they don't try to sleep, such as when they're watching TV or reading.

• Eating too much too late in the evening. Having a light snack before bedtime is OK, but eating too much may cause you to feel physically uncomfortable while lying down, making it difficult to get to sleep. Many people also experience heartburn, a backflow of food from the stomach to the esophagus after eating. This uncomfortable feeling may keep you awake.

• Inherited condition. Some people have inherited poor sleep tendency. If that's your case, be extremely careful not to overexcite yourself, especially in the evening.

• Anxiety

• Bruxism

• Depression

• Fibromyalgia

• high blood pressure

• Restless legs

• Sleep apnea

Insomnia becomes more prevalent with age. As you get older, three changes often occur that may affect your sleep. You may experience:

• A change in sleep patterns. After age 50, sleep often becomes less restful. You spend more time in stages 1 and 2 of non-rapid eye movement (NREM) sleep and less time in stages 3 and 4. Stage 1 is transitional sleep, stage 2 is light sleep, and stages 3 and 4 are deep (delta) sleep, the most restful kind. Because you're sleeping lighter, you're also more likely to wake up. With age, your internal clock often speeds up. You get tired earlier in the evening and consequently wake up earlier in the morning.

• A change in activity. You may be less physically or socially active. Activity helps promote a good night's sleep. You may also have more free time and, because of that, drink more caffeine or alcohol or take a daily nap. These things can also interfere with sleep at night.

• A change in health. The chronic pain of conditions such as arthritis or back problems as well as depression, anxiety and stress can interfere with sleep. Older men often develop noncancerous enlargement of the prostate gland (benign prostatic hyperplasia), which can cause the need to urinate frequently, interrupting sleep. In women, hot flashes that accompany menopause can be equally disruptive. Other sleep-related disorders, such as sleep apnea and restless legs syndrome, also become more common with age. Sleep apnea causes you to stop breathing periodically throughout the night and then awaken. Restless legs syndrome causes unpleasant aches in your legs and an almost irresistible desire to move them, which may prevent you from falling asleep.

Sleep problems can be a problem for children and teenagers, as well. In addition to many of the same causes of insomnia as those of adults, younger people may have trouble sleeping because of conditions such sleepwalking, night terrors or bruxism — teeth grinding. In addition, some children and teenagers simply have trouble getting to sleep or resist a regular bedtime, often because their inherent (circadian) clock is slow. When the clock on the wall says it's 10 p.m., their bodies may feel like it's only 8 p.m., because of their slow clock.

When to seek medical advice

If insomnia has been severely interfering with your daytime functioning for a month or longer, see your doctor to determine what might be the cause of your sleep problem and how it might be treated.

Screening and diagnosis

Insomnia may be difficult to diagnose because of its partly subjective nature and because so many factors can affect your sleep. Also, the kind of sleep patterns and degree of daytime fatigue that some people might consider to be indications of insomnia other people would not.

• Bruxism

• Fatigue

• Sleep apnea

Your doctor may ask you questions about your sleep patterns, such as how long you've experienced your symptoms and whether they occur every night. Your doctor may also ask about whether you snore, how well you function during the day, whether you take any medications and whether you have other health disorders. You may be asked to complete a questionnaire to determine your wake-sleep pattern and your level of daytime sleepiness.

If your complaint is insomnia, your doctor will only rarely suggest you spend a night at a sleep disorders center. These centers are accredited by the American Academy of Sleep Medicine. A team of people at the center can monitor and record a variety of body activities during the night, including brain waves, breathing, heartbeat, eye movements and body movements. But for most people whose main complaint is insomnia, their sleep is usually so distorted by the laboratory environment that doctors can learn little useful information.