On November 1, most of the United States will turn its clocks back by one hour. At 2 a.m. local time, clocks will return to 1 a.m. as daylight saving time ends and standard time begins.
That means Sunday will technically last 25 hours. Smartphones and other connected devices will usually update themselves. Traditional clocks may need to be changed by hand.
But there is one clock that cannot be reset with a button: the one inside your body.
The body follows a roughly 24-hour cycle called the circadian rhythm. This internal clock helps control when people feel awake and when they become sleepy. It is guided mainly by light and darkness.
Morning light tells the brain that it is time to become alert. In the evening, darkness encourages the body to produce melatonin, a hormone that helps people feel sleepy. When the time on the clock suddenly changes, the timing of sunlight, work, school, and meals changes with it.
Returning to standard time is generally easier than moving the clocks forward in spring. People do not lose an hour of sleep, and some may sleep a little longer.
However, the extra hour does not guarantee that everyone will wake up feeling rested. Some people may stay up later because they know they have more time. Others may wake according to their old schedule or feel sleepy earlier when darkness arrives sooner.
People who already sleep too little or work irregular hours may find the change more difficult. The darker afternoons can also leave some people feeling tired during their journey home.
Most people will adjust within a few days. Getting natural light in the morning can help the body reset its internal clock. Experts also recommend keeping regular sleeping and waking times, even on weekends. Opening the curtains or taking a morning walk may make the transition easier.
Not every part of the United States changes its clocks. Hawaii and most of Arizona remain on standard time throughout the year.
For everyone else, the clock will change in an instant. The body may simply need a little longer to catch up.