Insomnia may be caused by physical illness, a stress-filled lifestyle, excessive caffeine consumption, or chronic pain; or it may simply be the result of poor sleeping habits, such as napping during the day and going to bed at irregular hours. It is often linked to alcohol or drug abuse and to certain medications. Psychological factors alone account for about half of all insomnias evaluated by sleep therapists. For example, stress brought on by situations like a troubled marriage, a chronically ill child, or an unrewarding job can disrupt sleep. Depression is one of the most common causes of insomnia, and people with anxiety, schizophrenia, and other psychiatric disorders may also sleep poorly.

Certain physical illnesses interfere with sleep, especially disorders of the heart, lungs, kidneys, liver, pancreas, and digestive system. Other important physical causes include heartburn, chronic pain, and breathing disorders, such as sleep apnea. Insomnia often accompanies menopause, when sleep is disrupted by hot flashes or night sweats. Abnormal blood sugar levels can cause people suffering from diabetes or low blood sugar to wake up during the night.

Your own habits and lifestyle may be impeding your sleep pattern. Sedentary behavior and keeping an erratic schedule can contribute to insomnia, as can overconsumption of caffeine and other stimulants, or alcohol and other depressants. Over-the-counter drugs and preion medications ?from some blood pressure and heart drugs to thyroid hormones ?can interfere with sleep, as can the accidental or deliberate misuse of sleeping pills, to say nothing of illegal drugs. There is even some evidence that using electric blankets can disrupt normal sleep.