Our bodies are programmed for two natural periods of sleepiness during a 24-hour day, no matter how much sleep we've had in the previous 24 hours. The primary period is between midnight and 7am, and a second period occurs in the mid-afternoon, between 1pm and 4pm.

Poor sleep is not a normal part of ageing. As we get older, we often get less sleep because our ability to sleep for long periods of time and get into the deep restful stages of sleep can decrease. Older people have more fragile sleep and are more easily disturbed by light, noise and pain. They also may have medical conditions that contribute to sleep problems.

Sleep needs vary from person to person, and they change throughout a person’s lifecycle. Preschool and infants children (aged three to six) need 11 to 13 hours of sleep per night. Newborns sleep up to 18 hours a day, and school-aged children (up to age 12) need 10 to 11 hours. Adolescents need about nine hours of sleep a night and most adults need seven to nine hours of sleep.

On average, we spend about two hours dreaming each night, or 20% to 25% of a night’s sleep. Some researchers think dreams are merely a byproduct of sleep, but others believe they’re important for mood regulation, problem solving and stress reduction.

Nightmares, which are dreams that cause high levels of distress or terror, occur more often when you are stressed or anxious. They are more likely to occur in the last third of the night and tend to be more common among children than adults.

Sleepwalking may include simply sitting up and appearing awake, or it may involve complex activities, such as moving furniture, going to the toilet, eating, or, in rare instances, driving. Sleepwalking occurs more often in children and appears to run in families.

The British Sleep Foundation campaigns for people to regard driving while tired as similar to driving while drunk. Research backs this up, indicating it’s comparable to driving over legal blood-alcohol levels. A 1999 Gallup survey on sleep disorders found 11% of those interviewed admitted to falling asleep while driving.

If you don’t get the amount of sleep your body needs (typically 7.5 to 8.5 hours per night for adults), you start to accumulate a “sleep debt.” You can pay off a debt of a few hours by getting extra sleep over the next week or so, which is why you may have such a strong urge to sleep in on Saturday mornings. However, if the debt remains unresolved and continues to mount, you could be at increased risk of accidents or injury.

In addition to blurred vision, not getting enough sleep can cause fatigue, irritability and an inability to concentrate. Because these can be symptoms of other conditions as well, it may be helpful to keep a sleep journal and discuss your issues with your GP.

Several studies have shown that not getting enough sleep or a decrease in sleep quality can affect appetite controls and lead to overeating. Long term-sleep problems have been linked to weight gain, diabetes and even a shorter length of life.

Poor sleep can contribute to heart disease and heart disease can interrupt sleep. Poor sleep also has been associated with high blood pressure and stroke. Experts believe that factors such as inflammation and stress play a role. For example with sleep apnoea, pauses in breathing during sleep and low oxygen levels stress the body and promote inflammation. 

Chronic insomnia is when a person has difficulty falling asleep or staying asleep for a period of four weeks or longer. Acute insomnia can last for a few nights to up to four weeks.

Breathing pauses associated with sleep apnoea often occur five to 30 times or more per hour and can last from a few seconds to a few minutes, resulting in poor sleep that makes you tired during the day. The most common type of sleep apnoea is obstructive sleep apnoea, which usually is caused by the airway collapsing or being blocked during sleep. Common signs of obstructive sleep apnoea include loud snoring, morning headaches, irritability, memory and concentration problems and a dry throat upon waking. Most people with sleep apnoea don’t know they have the condition and it often goes undiagnosed.

The first state of sleep is NREM sleep, and it consists of four stages (light sleep, onset of sleep and two stages of deep, restorative sleep). During these stages, the muscles of the eyes are relaxed. The second state, REM sleep, is associated with increased contraction of the eye muscles. Both types are necessary for quality sleep.