Meditation simply refers to the process of subjecting oneself to a relaxed state of mind. This process is usually accompanied by a level of concentration and breathing. Meditation usually deals with our conscious and subconscious mind, and it starts with our conscious mind until the subconscious state of mind is achieved.
Sleep, on the other hand, is the resting period for both humans and animals, and it is usually characterized by a state of reduced consciousness. When we sleep, our subconscious mind takes up the job. Meditation can be in different forms, such as body scan, Zen, mindfulness, but sleep has about five different stages, such as light sleep, preparation for deep sleep, deep sleep, etc.
Meditation usually lasts for a few minutes, though, for some, it can last for hours. However, sleep can take several hours, usually around seven to eight hours. While sleep usually comes naturally, you will need a level of concentration for meditation.