Thank you for asking question on such a commonly encountered scenario at the clinic. At the outset, may I qualify that it will be important to distinguish between fatigue and daytime sleepiness. Patients who are tired need to rest and their sense of exhaustion will go away whereas for patients who are sleep deprived, they do need to have sleep to overcome their sleepiness.
The commonest cause of daytime sleepiness is insomnia at night. These people could not sleep well at night and hence they feel sleepy in the daytime. Many individuals with anxiety and depression do not sleep well at night. Alcohol use can lead to sleep fragmentation and hence these individuals do not find their sleep at night refreshing. Many persons are troubled by nocturia (need to wake up to pass urine) which interferes with their ability to get a good night's sleep.
Another common reason for daytime sleepiness is that of obstructive sleep apnea. These persons snore loudly in their sleep and their sleep is interrupted by frequent waking up, cessation of breathing and gasping for air. Many individuals are overweight or obese but I have come across individuals with normal BMI who have severe OSA; the condition is related to our craniofacial structures.
Other common causes of daytime sleepiness include anxiety, depression, narcolepsy, other medical problems like hypothyroidism, side effects of medicines, etc.
I hope you will take the necessary step of seeking treatment from a doctor who is interested in sleep medicine.
