Medications for treating insomnia are known as sedative-hypnotics or simply hypnotics. With insomnia, the person may have difficulty in falling asleep or staying asleep or may not feel fresh after sleeping. Frequently insomnia is caused by worry, tension and stress of daily life. Sleeping difficulties may occur with physical pain, discomfort, or illness. Certain medications and substances including alcohol, stimulants, caffeine selective serotonin reuptake inhibitor, antidepressants and illicit drugs can cause insomnia or upset sleep rhythm and disturb the quality of sleep. Some individuals have prior sleep disorder that cause sleep disruption, resultant in excessive sleepiness during the day and wakefulness at night. Sleep apnea, for example is a breathing-related sleep disorder in which the sleeping patient stops breathing during the respiratory cycle and then suddenly snorts and gasps for air the next moment. This stops breathing rhythm and prevents the person from getting a restful sleep. Insomnia may also be a symptom of an underlying mental disorder. Depressed individuals, for example, have characteristics changes in their sleep pattern and they may have marked difficulty in falling asleep, sleep too much, sleep fitfully after falling asleep or experience early morning awakening.