Simplify the following text for a Grade 12 native English-speaking person.
Original: Examples of sleep disorders are narcolepsy , sleep apnea and circadian rhythm sleep disorders .
Simplified: Homeostatic sleep propensity ( the need for sleep as a function of the amount of time elapsed since the last adequate sleep episode ) must be balanced against the circadian element for satisfactory sleep . Along with corresponding messages from the circadian clock , this tells the body it needs to sleep .