The amount of sleep that a person needs is dependent on a number of factors. First, his or her age. Babies, for instance, tend to sleep many hours in day. Second, the amount of aerobic activities that he or she does in the daytime. Odd job labourers and sportsmen tend to sleep more hours and have more deep sleep at night. Third, there are also individual variations in that some individuals may require more hours of sleep to feel refreshed.
Some individuals with obstructive sleep apnea may have interrupted sleep throughout the night (because of obstruction of the airway) and hence lack deep sleep. They hence prefer to sleep longer. Depressed individuals may not sleep well and hence would lie in bed for more hours in an attempt to compensate. There is also a type of depression, called major depression with atypical features, in that these patients will tend to sleep for more hours. The sleep changes are are part of depression.
Some people spend many hours in bed but they may do other things in bed apart from sleeping. For instance, they will lie in bed thinking about their problems and the multiple tasks that they need to perform the next day. Such behaviour is not compatible with sleep and over time, the individual may develop insomnia problem, as the mind starts to associate the bedroom and bed with thinking and worrying, rather than with sleep. Insomnia problem may subsequently lead to depression.