This can happen to you too.
A flight to catch or an important meeting is something you think about when you go to bed. You wake up on your own the next morning and discover you've beaten your alarm clock.
What is happening here? Is it lucky? Maybe you have the ability to wake up on time.
Many people have been to Dr. Stickgold to ask about this phenomenon.
Stickgold is a cognitive neuroscientist at Harvard Medical School and Beth Israel Deaconess Medical Center.
When Stickgold was just starting out in the field, he brought it up to his mentor, but he was greeted with a skeptical look. He assures you that all of the sleep researchers saybalderdash is impossible.
Stickgold thinks there is something to it. He says it's reported by hundreds and thousands of people. I can wake my wife up before she wakes up. Sometimes.
Humans have a system of internal processes that help us keep time. When we go to bed and wake up, these processes are influenced by our exposure to sunlight, coffee, exercise and other things, and this affects when we go to bed and wake up.
Philip Gehrman, a sleep scientist at the University of Pennsylvania, says you should wake up the same time every morning if you are getting enough sleep.
It doesn't make sense that you wake up a few minutes before your alarm when it's not your normal time.
He hears it all the time. I think it's the fear of being late that's contributing.
Over the years, some scientists have looked into this mystery.
The subjects in the study were able to wake up within 20 minutes of the target more than half the time. Two subjects who did the best were followed for another week. A small experiment showed that half of the awakenings were within seven minutes of the participants' written choices when they woke up.
People are asked if they have the ability to wake up at a certain time. More than half of the people said they could do this. It's possible that like a lot of things that we think we do a lot, we only do it once in a while.
The scientific evidence is not quite overwhelming.
There was an intriguing line of evidence that caught my attention thanks to Dr. Zee.
A group of researchers in Germany wanted to figure out how expecting to wake up influenced the HPA axis, a complex system in the body that deals with our response to stress.
Jan Born, one of the study's authors, says they knew that levels of a hormone that's stored in the pituitary glands start increasing in advance of the time you habitually wake up.
In this case, we decided to try it out and it came out as hypothesis.
Born and his team found 15 people who would normally wake up around 7 or 7:30 a.m., put them in a sleep lab and took blood samples.
Five of the subjects were told to get up at 6 a.m., while others were told to wake up at 9 a.m.
As their wake-up time approached, a clear difference emerged.
The subjects who expected to wake up at 6 a.m. had a noticeable increase in their concentration. It was as if their bodies knew they had to go to sleep.
"You can make it until you have your first coffee if you get up early," says Born with a laugh.
Members of the group who did not plan to wake up early were surprised by a 6 a.m wake up call. It was too late in the morning to see the same effect as the third group, which was assigned a 9 am wake up time.
The findings of Born's experiment raise some intriguing questions about when people will wake up on their own. How did they know that they needed to get up earlier?
He says that the system is plastic and can change in time. It shows that we have the ability to exploit this system while awake. He says that idea is not new in sleep research.
According to Born, there is a mechanism in the brain that can be used to influence your body while you sleep. He points to research that shows that a suggestion can make someone sleepy.
Some people are able to wake up without an alarm clock because of multiple biological systems. She says it's possible that the worry about getting up is overblown.
She says that the paper shows that your brain is still active.
Exactly how it's working and how much you can rely on it remains a big unanswered question. Harvard's Stickgold isn't ready to dismiss the question of whether sleep researchers will ditch their alarm clocks.
He says that it's a true scientific mystery. It would be arrogant to assume that it can't happen since we don't know how it happened.
This story is part of NPR's periodic science series, "Finding Time."
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