Almost everyone has felt drowsy before, usually due to normal tiredness from a long day or lack of sleep. There are other causes of this condition as well. Most of the causes are not serious, but some are life threatening.
Sleep apnea is a disorder of breathing during sleep that prevents a person from getting enough rest.
Other causes are also possible. Sometimes no cause can be found. Avoiding stress and overexertion, getting enough sleep, and eating a healthy diet can prevent many cases of drowsiness. Avoidance of alcohol and medications that cause drowsiness can avoid cases due to these causes. Maintaining a normal weight and avoiding obesity can sometimes prevent sleep apnea .