Chronic sleep deprivation can interfere with balance, coordination, and decision-making abilities. You’re at risk falling asleep during the day, even if you fight it. Stimulants like caffeine are not able to override your body’s profound need for sleep. (source)
Insomnia can be caused due to stress and strain. Professional, personal, emotional, physical and mental worries can contribute to you undergoing a sleepless night. Such an occurrence happening once in a blue moon should not be a cause of worry. However, if you find you getting much less than your eight hours recommended normal quota of sleep every night for more than five days running, it is time to see a doctor.
A change in lifestyle can also prevent you from sleeping.
Did you go to bed too soon after a heavy meal? Are your surroundings noisy? Is your bed lumpy and your mattress too soft or too hard? These are just some of the reasons why you may not find it easy to drop off to sleep the moment you get into your bed. You should be asleep within 7 to 10 minutes in a normal sleep routine cycle.