The most common cause of obstructive sleep apnea in adults is obesity and excess weight. This is associated with excess soft tissue in your mouth and throat. Once your tongue and throat tissues relax when you fall asleep, your airway can become blocked. You then wake up briefly choking and gasping for air, and once your airway is unblocked you fall asleep again. Each episode can take 1-3 seconds long, and you can experience up to 50 or more such awakenings each night (sometimes over 100) without being aware of them.