Insomnia

Sleeplessness. Feeling you aren't getting enough sleep despite an adequate opportunity to sleep.
Trouble falling asleep or staying asleep.

Three types of Insomnia:

TRANSIENT insomnia lasts no more than a few nights and is usually triggered by a change in sleep schedule, excitement, stress, or a brief illness.
SHORT-TERM insomnia lasts about 2-3 weeks and is usually related to stress or medical or psychiatric illness.
LONG-TERM OR CRONIC insomnia lasts longer than a few weeks, with poor sleep every night, most nights, or several nights per month.

Causes

Lifestyle factors - Drugs/medications, drinking caffeine-containing beverages, and /or alcohol can result in poor sleep. Varying bedtimes from night to night and changing work shifts can undermine sleep quality.
Environmental Factors - Noise, lighting, and extremes in room temperature can interfere with sleep.
Physical Factors - Primary sleep disorders, such as sleep apnea are associated with chronic insomnia. Illness, pain, and itching may also upset sleep.
Psychological Factors - Insomnia is a common symptom of depression. Stress, anxiety, and tension interfere with sleep.

Prevention

Sleep needs vary for different people. Most individuals need 6-9 hours of sleep; however, there are a few people who require only 4-5 hours. Go to bed when you are sleepy, and use your bed for sleeping only, not as an office or a place to watch TV.
Establish a sleep pattern. Try getting up at the same time every day, even if this means you miss a little sleep once in a while. Most people can bounce back from a lost 1-2 hours without any noticeable difference in performance.
Avoid caffeine within seven hours of bedtime. Avoid alcohol and smoking 1-2 hours before bedtime.
If you are a bedtime "worrier", dedicate another time - perhaps 30 minutes after dinner - to write down problems and possible solutions.

Self-care

Exercise regularly. Get vigorous exercise in the late afternoon or early evening. Don't exercise before sleep as this may impair your ability to sleep.