Many causes can cause the constant desire to sleep and drowsiness during the day. The first is poor sleep habits, such as lack of sleep at night or irregular sleep schedules. Some people also have sleep disorders, such as short periods of respiratory arrest during sleep, also known as sleep apnea syndrome. Some people have episodes of sleepiness, where they are very sleepy during the day and sometimes fall asleep suddenly in the middle of normal activities, or they have insomnia that causes them to want to sleep all the time, such as difficulty falling asleep or waking up early. Certain disorders can also present with constant sleepiness, such as hypothyroidism, due to the inability to produce adequate amounts of thyroid hormones, hormones that control the body’s storage and use of energy. In the case of chronic depression, it affects work and the processing of daily life due to feeling sad and depressed most of the time. There are some factors that affect in sleep, such as sounds, or your own health problems, such as leg cramps at night, frequent night shifts and constant change of time zones. Certain medications may also have an effect causing the constant desire to sleep, and the doctor will recommend the appropriate treatment depending on the cause.