Sleep apnea is a breathing disorder characterized by episodes of disturbed or interrupted breathing during sleep resulting in recurrent arousals and awakenings.

The symptoms of sleep apnea are loud snoring, hyper somnolence (excessive daytime sleepiness), and restless sleep.

Snoring is a sign of upper-airway obstruction to a critical degree. During snoring the inability to inhale oxygen and exhale carbon dioxide upsets the balance of oxygen and carbon dioxide in the blood. The brain senses the low level of oxygen and increased levels of carbon dioxide and sends a signal to resume breathing and cause an arousal. The frequent arousals inhibit the normal sleep cycle and results in fragmented sleep. This makes the patient feel very sleepy during the day and complain of a very unrefreshing sleep at night.

The problem of excessive daytime sleepiness (especially while driving, working or talking) develops slowly over years and often gets noticed by the friends and colleagues of the patient.

In central sleep apnea, the hypoxic and hypercapnic drives can be impaired by brain stem lesions or by exposure to recurrent hypoxia and hypercapnia. The stimulus to breathe instead from the cortex and reticular activating system is lost during sleep and the patient stops breathing, the so-called "Ondine's curse".

Other symptoms of sleep apnea include choking/gasping during sleep, morning headaches, daytime fatigue, personality changes, memory impairment, impaired concentration, poor judgment, mood disturbances, recent weight gain, polyurea, and impotence.

The signs and symptoms that can help identify patients at risk for sleep apnea are obesity, senility, stress (including anxiety and depression), hypertension, cardiac arrhythmia, ischemic heart disease, hypothyroidism, acromegaly, dislocated temporomandibular joint and neuromuscular disease. In children, tonsillar hypertrophy is the commonest cause for sleep apnea.