The need for sleep can increase or decrease depending on the state of the body at any given time. The desire to increase sleep duration is generally an indication of fatigue.
Fatigue is a multifaceted issue that can be the symptom of: illness in the form of a simple cold or a sinister pathology such as cancer, energy deficiency due to poor nutrition, a lack of exercise and emotional stress or a side effect from medication just to name a few.
Increased sleep requirements due to exercise can occur due to the following reasons: too much exercise (overtraining) and/or a lack of exercise creating a state of lethargy.
Some drugs in a bid to alleviate conditions or health problems may cause lethargy, creating a false need for sleep.
Just as the body can desire a need for increased sleep, the opposite can also occur.
Generally a decrease in sleep requirement stems from the body functioning efficiently due to increased energy levels stemming from better lifestyle choices (exercise, quality food, etc.).
Another reason all be it a pseudo one is the use of stimulants. Stimulants such as coffee increase short term energy levels creating a false sense of vitality and a decreased need for sleep.
TOH deems that energy derived from long term consumption of natural or synthetic stimulates will eventually cause malfunction of the mind and body. Continuous long term sources of energy should be derived from natural whole foods.