Normally during sleep, the throat muscles will keep the throat open and air flows through it to the lungs. Any obstacle in this can cause sleep apnea. These obstacles may be due to the blockage of the breathing passage by tonsils and adenoids. With the throat frequently fully or partly blocked during sleep, enough air cannot flow into the lungs through the mouth and nose even though you efforts to breathe continue. When this happens, the amount of oxygen in your blood may drop. Normally breathing may become hard and noisy and may even stop for short periods of time.

The two distinct forms of sleep apnea are Obstructive and Central.

The most common type, obstructive sleep apnea (OSA) is caused by the blockage of airways. The windpipe (called the trachea) that brings air into the body might be blocked by the tongue, tonsils or uvula (the little piece of flesh that hangs down in the back of your throat). The blockage may also be caused by the large amount of fatty tissues in the throat or even by relaxed throat muscles. When these muscles relax, the airway narrows or closes as you breathe in, and breathing is cut off momentarily. This may lower the oxygen level in the blood.

The rare type, central sleep apnea occurs when the brain that controls the breathing doesn't send proper signals to the breathing muscles. Snoring does not occur in this type, as it is not caused by the blockage of airways. The most common cause of central sleep apnea is heart disease.

There is also another type known as complex sleep apnea. As the name suggest, this form is the combination of both obstructive and central sleep apneas.