Circadian rhythm is your internal clock. Certain brain structures and chemicals produce the difference between the state of sleeping and waking. This rhythm is developed in the first months of life. It controls the daily ups and downs of biological patterns, including body temperature, blood pressure, and the release of hormones.

Several components make up your body’s circadian rhythm.

• Light plays a major role in your internal clock. Your brain will respond to light and dark by sending signals that activate the functions that make you more tired or alert.
• The amount of melatonin you have can either increase or decrease.
• Your body temperature and metabolism also play a part. When you sleep, your body temperature drops and then rises again when you’re awake.

Most adults reach their most tired phases of the day from 2 to 4 a.m. and 1 to 3 p.m. Your circadian rhythm changes with age, and once you’re older, you may find yourself going to bed earlier and waking up earlier. This is a normal part of aging.

How it gets out of sync:

Your circadian rhythm can become out of sync and that’s due to irregularities in your lifestyle such as:

• Overnight or off-hours work shifts that go against the natural light and dark times of the day.
• Work shifts with erratic hours.
• Travel that spans the course of one or more different time zones.
• A lifestyle that encourages late-night hours or early wake times.
• Medications you take.
• Stress.
• Mental health conditions.
• Health conditions like brain damage, dementia, head injuries, or blindness.
• Poor sleep habits, including lacking a sleep schedule, eating, or drinking late at night, watching screens too close to bedtime, or not having a comfortable sleeping space.

How to reset:

• Try to adhere to a routine each day.
• Spend time outdoors when it’s light outside to boost your wakefulness.
• Get enough daily exercise — twenty or more minutes of aerobic exercise is generally recommended.
• Sleep in an environment that promotes rest with proper lighting, a comfortable temperature, and a supportive mattress.
• Avoid alcohol, caffeine, and nicotine in the evenings.
• Power down your screens well before bedtime and try engaging in something analog, such as reading a book or meditating.
• Do not nap late in the afternoon or evening.