Obesity is related to the following sleep conditions.

Sleep deprivation and fragmentation
Sleep deprivation and fragmentation lead to insulin resistance and other hormonal and autonomic changes with the result that appetite is increased and obesity and the ‘metabolic syndrome’ often develop.

Obstructive sleep apnoeas
Obstructive sleep apnoeas are caused by obesity and may also contribute to it through inducing the metabolic syndrome with insulin resistance, diabetes mellitus, an increase in lipids and hypertension. The serum leptin is raised due to increased sympathetic activity both during the day and at night, but falls once effective CPAP treatment is started.

Narcolepsy
An increase in appetite, particularly for carbohydrates, is common at the onset of symptoms, but later in the natural history food intake appears to be reduced, although some subjects retain a craving for carbohydrate food during the night. Carbohydrates in general appear to have an increased tendency to promote sleep in narcolepsy.

The serum leptin level is reduced, probably because of a reduction in sympathetic activity, and there is also loss of the nocturnal increase in leptin.

Kleine–Levin syndrome
The episodes of hypersomnia are commonly associated with a voracious non-selective appetite.

Sleep eating and drinking
This commonly causes obesity.

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