Everyone's experienced the fatigue, short temper and lack of focus that often follow a poor night's sleep.

An occasional night without sleep makes you feel tired and irritable the next day, but it won't harm your health.

After several sleepless nights, the mental effects become more serious. Your brain will fog, making it difficult to concentrate and make decisions. You'll start to feel down, and may fall asleep during the day. Your risk of injury and accidents at home, work and on the road also increases.

If it continues, lack of sleep can affect your overall health and make you prone to serious medical conditions, such as obesity, heart disease, high blood pressure and diabetes.