People with delayed sleep phase fall asleep and wake later than they want and later than usual sleep and wake times. Sleep and wake times are delayed at least two hours and may be delayed up to 3 to 6 hours. People with delayed sleep phase may regularly go to sleep at 3 a.m. and wake at 10 a.m., for example.

Symptoms are persistent. They last at least three months and often for years. Symptoms may include:

• Not being able to fall asleep at a typical bedtime, known as insomnia.
• Trouble waking up in the morning in time to go to work or school.
• Extreme daytime drowsiness.
• Trouble staying alert during the day.

When to see a doctor

See a health care professional if you have persistent symptoms of delayed sleep-wake phase disorder. Or make an appointment for your child if you think your child has symptoms of delayed sleep-wake phase disorder that don't go away.

Also make an appointment if you or your child regularly has trouble waking in the morning or has excessive daytime drowsiness.

Delayed sleep phase is caused by a person's internal clock being out of sync with the environment. Your internal clock lets you know when it's time to sleep and when it's time to wake. Known as circadian rhythm, your internal clock is on a 24-hour cycle. Cues in the environment influence the sleep-wake cycle. These cues include light, darkness, eating and physical activity.

The exact cause of delayed sleep phase isn't known. But circadian rhythms can be delayed in teenagers for biological reasons. Staying up late to do homework, watch TV or use the internet can make the sleep delay worse.

Delayed sleep phase can affect children and adults of any age. However, delayed sleep phase is more common among teenagers and young adults.

To diagnose delayed sleep phase, also known as delayed sleep-wake phase disorder, a health care professional reviews your family and medical history. You also may have a physical exam.

You may need several tests to diagnose delayed sleep phase or any related conditions, such as:

• Actigraphy. This test tracks your sleep and wake times over several days. During the test, you wear a small device on your wrist that detects your motions. The device also may monitor light exposure.
• Sleep diary. You may need to keep a sleep diary for a week or longer. Log your daily sleep and wake times to understand your sleep pattern.
• Sleep study, also known as polysomnography. If it's suspected that you might have an additional sleep disorder, you may need a sleep study. In this test, you stay in a sleep center overnight. Polysomnography monitors your brain activity, heart rate, oxygen levels, eye movements and breathing function as you sleep.

A health care professional works with you to create a treatment plan that can help adjust your sleep and wake times.

Your plan may include:

• Improving sleep habits. Making lifestyle changes can improve your sleep habits. This is known as sleep hygiene. To practice good sleep hygiene, go to bed and wake on a regular schedule, including on the weekends. It's best not to take naps during the day. Don't drink caffeine or alcohol near bedtime. And don't use tobacco products.

  Exercising during the day also helps improve sleep, but schedule exercise to finish at least two hours before bedtime. It's also helpful not to engage in stimulating activities near bedtime. Use your bedroom only for sleeping and sex.

• Melatonin supplements. Melatonin is a hormone that plays a role in the sleep-wake cycle. You may be prescribed a melatonin supplement to take in the early evening. This can help adjust your circadian rhythm to go to sleep earlier.
• Light therapy. Light exposure using a light box in the morning may adjust your circadian rhythm.
• Chronotherapy. For some people, health care professionals prescribe a sleep schedule that delays bedtime by 1 to 2.5 hours every six days. This is done until the desired bedtime is reached. You need to maintain your sleep schedule once it is established.