Daytime sleepiness can indicate that a person is suffering from a sleep disorder that interrupts their circadian rhythms and prevents them from getting enough sleep.
You can cheat on the amount of sleep you get
Continuously getting inadequate or no sleep can result in a “sleep debt,” which builds over time and eventually interferes with nightly sleep, as well as having numerous implications for one’s health and life (link to body page)
Staying up late to cram before an exam can make up for poor time management and study habits.
Cramming does not make up for poor study habits throughout the year due to being highly stressful and not a sure way of retaining information. Additionally, the brain makes new neuron connections and prunes old ones while the body is asleep, and cutting back on sleep decreases the amount of material that is retained.
The older you get, the less sleep you need
While adults need less sleep than young children do, they still need about 7-9 hours of sleep each night. Adults failing to get enough sleep are prone to poor job performance, the possibility of auto accidents as a result of drowsiness, emotional volatility that can end friendships and marriages, and other things.
Changing the times you go to sleep and wake up can easily make up for lost time
Getting a regular amount of sleep each night is important to keeping the body’s circadian rhythm, and maintaining appropriate sleep-wake cycles. Changing the body’s sleep schedule too much can disrupt this rhythm and interfere with the body’s ability to get to sleep.
Caffeine can remedy a lack of sleep
Caffeine only provides a temporary energy boost to the consumer, which quickly wears off. Consuming caffeine within six hours of going to bed can result in a disrupted sleep schedule.
Sources
-James Maas, Power Sleep
-National Sleep Foundation
-About.Com: Sleep Disorders