Obesity is frequently complicated by many medical problems. Typically, as people gain weight, they tend to feel tired all the time and may have problems sleeping. Problems with sleep may be indicative of a severe condition called Pickwickian Syndrome, or sleep apnea. For people with this problem, it becomes progressively more difficult to breathe at night as their weight increases. These people typically snore severely and have episodes when they stop breathing completely for up to one minute at a time. During these periods of not breathing, their heart rates may become very irregular, which can lead to fatal heart attacks. Frequently, these people transiently awaken when they resume breathing. This may occur dozens of times per night, causing them to feel tired the next day and even fall asleep while sitting in meetings or driving. Sleep apnea is a very serious complication of obesity and requires professional medical attention.

Research shows that interrupted sleep can actually contribute to weight increases. Patients who got the least REM sleep were the heaviest. They also found that patients who got more REM sleep after treatment lost weight, and that those who showed the biggest increases in REM sleep lost the most weight. Sleep apnea contributes to weight gain, at least in part, by disrupting REM sleep.