How much sleep do you need?

It's about time
How sleepy you are depends largely on how well you've been sleeping and how much sleep you've been getting. Another key factor is your internal "biological clock"—a tiny bundle of cells in your brain that responds to light signals through your eyes and promotes wakefulness. Because of the timing of the biological clock and other bodily processes, you naturally feel drowsy between midnight and 7 a.m. and again in the midafternoon between 1 p.m. and 4 p.m.
Night shift workers often find themselves drowsy at work. They also have trouble falling asleep or staying asleep during the day, when their schedules require them to sleep. Being sleepy puts them at risk for injuries on the road and at work. Night shift workers are also more likely to have conditions such as heart disease, digestive disorders, and infertility, as well as emotional problems. All of these problems may be related, at least in part, to their chronic lack of sleep.
Adapting to a new sleep and wake times can also be hard for travelers crossing time zones, resulting in what's known as jet lag. Jet lag can lead to daytime sleepiness, trouble falling asleep or staying asleep at night, poor concentration, and irritability.
The good news is that by using appropriately timed cues, most people can change their biological clock, but only by 1–2 hours per day at best. Therefore, it can take several days to adjust to a new time zone (or different work schedule). If you'll be moving across time zones, you might want to begin adapting to the new time zone a few days before leaving. Or, if you are traveling for just a few days, you might want to stick with your original sleep schedule and not try to adjust to the new time zone.