Symptoms. Include not being able to fall asleep at a "normal" time. A lot of patients can't fall asleep before 2-6 am. As a result, you can't wake up before 10 am to 1 pm. If you must get up, you feel sleepy/tired till late afternoon. These things reduce your ability to function, leading to job and relationship problems.
Night owls. This is the technical term to describe people who have trouble going to sleep at a socially acceptable time, sleep a normal amount but have trouble waking up in the mornings. Some people's sleep onset keeps advancing, casing major social difficulties. Sleep hygiene, melatonin and careful attention to light exposure can be very helpful.