The act of walking to the bed, lying down in it, and shutting your eyes for the purpose of sleep.
Some people often find themselves unwilling to do this, because they have something far more important at hand that requires them to keep staying awake. Such tasks often involve programming, chatting, partying or paranoia.
However, partying can sometimes lead to the desire to go to bed for other reasons than sleep (See things to do in bed).
When people do go to bed, and sleep, they often find themselves equally unwilling to get out of bed. People making the decision to stay in bed, often refer to this as beauty sleep.