sleep deprivation

I think it is absolutely paradoxical. At school, teachers say if we sleep more than 5 hours, we won't do well on school work. it confused me. How much is enough? How well am I sleeping?
I sometimes felt sleepy during very important test. I knew I should not have been sleepy and should have concentrated on what I was doing, but it was not that easy. My mom just scolded me it's all because my spiritual strength was too weak or I was out of my mind. Actually, No one can be sleepy, knowingly. but after I looked into "Sleep-deprived", I diagnosed myself i'm having trouble with sleep.
According to an FDA article, it is normal to feel tired every now and then during the day but it is not normal for fatigue to interfere with routine activities. For example, you shouldn't be dozing off while reading the newspaper, during business meetings and so on.
I think the reasons for my sleepiness are various. The times I sleep everyday are irregular and I often eat less than 2 hours before I go to bed. Sleep deprivation includes symptoms of insomnia, sleepiness during the day and snoring.
Insomnia is considered chronic when it lasts most nights for a few weeks or more. This longer-term condition deserves professional insomnia or not, experts suggest looking at it like a headache. Doctors say "If you goes on day after day and nothing you do makes it go away, then you should see a doctor."
Like I experience, sleepiness during the day is really irritating. Unlike insomnia, people who fall asleep in less than five minutes may have a serious sleeping disorder called narcolepsy. from now on, I'll try and make better sleep habits.
Here are some tips:
Keep a regular sleep-wake cycle. Try to go to bed and wake up at the same time everyday.
Avoid caffeine, alcohol, and nicotine in the four to six hours before bedtime.
Don't exercise within 2 hours of bedtime. Exercising five or six hours before bedtime may help you sleep more soundly.
Don't eat large meals within tow hours of bedtime.