特别累的时候都想好好休息一番，可有时却怎么也睡不着，这让人非常痛苦。怎样才能解决这个让人头痛的问题呢？看看下面这篇文章的说法吧！

    Why is it so difficult to fall asleep when you are overtired? There is no one answer that applies to every individual. But many people fail to note the distinction between fatigue -- physical tiredness -- and sleepiness, the inability to stay awake. It's possible to feel "tired" physically and still be unable to fall asleep, because while your body may be exhausted, you don't feel sleepy. To fall asleep, you need adequate time to unwind, even if you feel fatigued. It's not so easy to simply "turn off." 

    Lack of sleep complicates matters even more. Experts say adults need at least 7 to 8 hours of sleep a night to function properly. When you get less sleep than that on consecutive nights, you begin to accrue "sleep debt." As sleep debt increases (and functionality decreases), your body experiences a stress response and begins to release adrenaline. Now a vicious cycle has been created: You experience the feeling of being more and more tired, but your body is increasingly stimulated. "Power sleeping" for more hours on weekends is only a temporary solution. There is no substitute for getting a good night's sleep on a regular basis. 

    unwind: 放松 

    accrue: 产生 

    adrenaline: 肾上腺素 

    vicious cycle: 恶性循环

    power sleeping: 补觉