Daylight saving time ends on Sunday. Time to “fall back” for an hour.

The good news: you'll get a wonderful extra hour of sleep. The Bad: It will be dark until late afternoon in the US for the next few months

Daylight saving time ends at 2 a.m. local time on Sunday, which means you should set your clocks back an hour before bed. Standard time will last until March 9th, then we will “spring forward” again with the return of Daylight Saving Time.

This change in spring can be more stressful for your body. Darker mornings and brighter evenings can throw your body clock out of whack, making it difficult for you to fall asleep on time for weeks or longer. Studies have even found an increase in heart attacks and strokes right after the time change in March.

“Fall back” should be easier. Still, it can take a while to adjust your sleep habits, not to mention the downsides of leaving work in the dark or trying to exercise while there's still enough light. Some people with seasonal affective disorder, a type of depression usually related to the shorter days and less sunlight of fall and winter, may also have problems.

Some health groups, including the American Medical Association and the American Academy of Sleep Medicine, have said it's time to do away with time changes and that sticking to standard time is more consistent with the sun – and human biology.

Most countries do not observe daylight saving time. For those who do – particularly in Europe and North America – the clock change date varies.

Two states – Arizona and Hawaii – do not change and remain on standard time.

Here's what you should know about the twice-yearly ritual.

How the body reacts to light
The brain has a master clock that is set by exposure to sunlight and darkness. This circadian rhythm is a roughly 24-hour cycle that determines when we become sleepy and when we are more alert. The patterns change with age, one reason early risers turn into hard-to-wake teenagers.

The morning light sets the rhythm anew. In the evening, levels of a hormone called melatonin begin to rise, causing sleepiness. Too much light in the evening – that extra hour compared to daylight saving time – delays this increase and the cycle gets thrown out of sync.

And this circadian clock influences more than just sleep, it also influences things like heart rate, blood pressure, stress hormones and metabolism.

How do time changes affect sleep?
Even a change in hours can disrupt your sleep schedule – because even if the clocks change, work and school start times remain the same.

This is a problem because so many people are already sleep deprived. Approximately one in three U.S. adults sleeps less than the recommended seven hours each night, and more than half of U.S. teenagers do not sleep the recommended eight hours during the week.

Lack of sleep is linked to heart disease, cognitive decline, obesity and numerous other problems.

How to prepare for the time change
Some people try to prepare for a time change by gradually changing their bedtimes in the days leading up to the time change. There are ways to make the transition easier, such as getting more sunshine to reset your circadian rhythm for healthy sleep.

Will the US ever abolish the time change?
Occasionally the legislature proposes to abolish the time change entirely. The most prominent recent effort, a now-stalled bipartisan bill called the Sunshine Protection Act, proposes making daylight saving time permanent. Health experts say lawmakers are getting it wrong — standard time should be made permanent.

Kentwood, Louisiana, dairy farmer Aubrey Jarrell is not a fan of the time change. He said it interferes with his cows' strict milking routine and causes them stress, “and stress is not good for a dairy cow.” Until they adapt, milk production will drop, he said.

“Keep the same time — whatever it may be — but keep it the same,” he said.

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