Overview

Delayed sleep phase — officially known as delayed sleep-wake phase sleep disorder — is an internal sleep clock (circadian rhythm) sleep disorder in which your sleep pattern is delayed two hours or more from a conventional sleep pattern, causing you to go to sleep later and wake up later.

Diagnosis

To diagnose your condition, your doctor may review your family and medical history and conduct a physical examination. Your doctor may order several tests to diagnose your condition or any other related conditions, such as:

• Actigraphy. In this test, you wear a small device that tracks your sleep-wake behavior at home.
• Sleep diary. Your doctor may ask you to keep a sleep diary in which you log your daily sleep and wake times to help show your sleep pattern.
• Polysomnogram. If your doctor suspects you have a different sleep disorder, he or she may order a polysomnogram. In this test, you stay in a sleep center overnight. A polysomnogram monitors your brain activity, heart rate, oxygen levels, eye movements and breathing function as you sleep.

Source: http://www.mayoclinic.com