Lack of rest and sleep could affect your job. Medically you are expected to have about eight hours of sleep during the night but most people could only afford four hours because they usually sleep very late..This is why I always believe that a person must emphasise a ,lot on his health initially and take such kind of matters seriously. A person must go to bed early so that he may not feel sleepy while he is at work. Most people feel sleepy because they do not sleep at the right time at night.