Sleep is essential for everyone, and we spend about one-third of our lives in bed. A healthy sleep helps us to recharge our batteries, both mentally and physically. A good night's sleep is the best way to cope with daily stress, work more efficiently and fight off illness.

1. What type of sleep do you need?
Many people think that sleep is a passive and unchanging process. In fact, the physical body rests during sleep, but the brain remains active. There are two basic states of sleep, rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep, which the brain organizes in a regular and cyclic manner. Sleep usually begins with 80 minutes of NREM sleep followed by 10 minutes of REM sleep with this cycle being repeated four to six times throughout the sleeping period. NREM sleep is characterized by a slowing down of the brain and body functions; REM sleep appears in brief intervals with increased activity in the brain and body. If the sequence is interrupted, such as by external stimuli, it will affect the quality of sleep. (See sleeping chart of a young adult.)

Sleeping chart of a young adult.

2. What happens if you do not sleep enough or do not sleep well?
Although the precise functions of sleep remain unclear, sleep is important for normal physical and mental functioning. We all recognize the need for sleep, of the lack of which leads to difficulty in concentration, memory lapses, low energy, fatigue and emotional instability. In the long term, sleep disturbances are associated with serious illnesses such as hypertension, heart disease, stroke, diabetes, obesity, psychiatric disorders, mental impairment and even growth retardation in children. Studies have demonstrated that brain activity declines significantly after 24 hours of sustained wakefulness; there is a decrease in body temperature as well as a decline in general immunity.

3. How much sleep is enough?
The amount of sleep needed varies from person to person, and changes throughout the lifecycle. Generally, newborns sleep about 16 to 18 hours a day; preschool children sleep between 10 and 12 hours; school-aged children and teenagers sleep at least 9 hours, while most adults sleep 7 to 8 hours on average. However, some people may need less or more than the average hours, the most important criteria for adequate sleep is waking up feeling completely refreshed. Most importantly, sleep should be uninterrupted. On awakening, you should feel alert and refreshed and there should be no drowsiness even when engaging in boring activities. If you feel drowsy while awake, you may not have had enough quality sleep.

4. Can you "cheat" on the amount of sleep?
On average, we need 7 to 9 hours sleep per day for optimal heath. When the daily sleep hours are less than an individual's needs, a "sleep debt" develops. This means the loss of sleep will eventually need to be repaid with additional sleep over the coming nights. Our body seems unable to adapt to sleep less than it needs. When the sleep debt becomes too great, it can lead to impaired body functioning. Caffeine and other stimulants cannot act as substitutes for sleep; they can only counteract some effects of sleep deprivation.

5. Do people need less sleep as they get older?
There is no evidence to show that older people need less sleep than younger people. In fact, older people don't need less sleep, but they often get less sleep. While sleep patterns change as we age, older people tend to spend less time in the deeper, restful stages of sleep. They are more easily awakened by light, noise, or pain. For elderly people, it takes longer to fall asleep, and the frequency and duration of overnight arousal increase. Therefore, they should stay longer in bed to ensure they have enough rest for ordinary everyday functioning.

6. Can the body adjust quickly to different sleep schedules?
Our body has an internal biological clock to regulate the sleep/wake cycle, which functions according to a normal day/night schedule. Traveling across time zones or working night shifts will confuse the body's sense of time that makes sleep difficult and inhibit some necessary sleep functions. The biological clock can be reset, but only by appropriately by one to two hours per day at best. It takes some time for our body to adjust to a new time schedule. The change in sleeping patterns may be reduced by measures like sleeping in a dark and quiet room, getting exposure to bright light at night time, and changing eating and exercise patterns.

7. Is dreaming good or bad?
On average, we spent about two hours dreaming every night and mostly during REM sleep. Experts believe that dreaming helps exercise certain brain functions, promote learning and memory, and even solve problems that require much concentration. Nightmares that occur in children and adults are often caused by stress, traumatic experiences, emotional problems, drugs or illness.

8. Do you have a sleep disorder?
Generally, if you find it difficult to fall asleep, cannot stay asleep through the night, wake up too early, have a hard time waking up, or are very tired during the day, you may suffer from a sleep disorder. When you experience the following symptoms for a month or more, it is recommended that you seek professional advice:

	take over 30 minutes to fall asleep every night;
	wake up several times at night and cannot go back to sleep;
	wake up too early in the morning;
	have vivid, dreamlike experiences while falling asleep;
	feel sleepy, have frequent naps or fall asleep at inappropriate times during the daytime;
	struggle to stay awake when inactive, such as while watching TV or reading;
	have difficulty in paying attention or concentrating at work, school or home;
	become emotional very easily.