When you can’t sleep even though you’re tired, to understand why, you may do well to look back through evolution to a time when people had no access to artificial light.

Did you know that even just four nights of poor sleep can wreak havoc on the way you eat and the way your body stores fat?

If you're not asleep by 11pm, you could be setting your body up for a 'second wind' which will keep you awake for even longer.