A sleep log is a way to track your sleep and gather details about your insomnia symptoms. If you work with a sleep specialist or are a patient in a sleep disorder clinic, your doctor will probably ask you to fill out a sleep log for one to two weeks to get a better understanding of your sleep troubles. Even if you talk to your regular doctor (rather than a specialist) about sleep troubles, this log will provide a more comprehensive picture of your recent sleep patterns.
Your doctor may use the information collected in your sleep diary along with other tests to diagnose and decide on a treatment recommendation for insomnia.
To get the most accurate information, fill out the sleep log as early in the morning as you can (so your bedtime routine and nighttime sleep are fresh in your memory). You may want to make this part of your morning routine. If it's more convenient for you, sleep diaries are also available as apps for your phone.