Your circadian rhythm (sleep-wake cycle) is most heavily influenced by light in your surrounding environment, but can also be affected by temperature, physical activity, and social interactions. When your body’s internal clock isn’t synchronized with these external cues, you may feel sleepy but still have trouble sleeping.

Your biological clock

There are many parts of your brain that pick up on these external cues like sunlight, which then initiate signals to be sent to a brain structure called the suprachiasmatic nucleus (SCN). The SCN uses this information to control many different processes in your body, such as digestion, hormone regulation, body temperature, and sleep.

Medically reviewed by

Dr. Colleen Ehrnstrom's profile picture
Dr. Colleen Ehrnstrom, PhD

Dr. Colleen Ehrnstrom is a licensed clinical psychologist with a specialty practice in Acceptance and Commitment Therapy (ACT). Areas of expertise include insomnia and other sleep disorders, anxiety, and depression.

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