For ever 2 hours you are awake, the average brain needs 1 hour of rest. The brain will force you to go to sleep in order to get the rest it needs, even if it means falling asleep at the wheel.
Rest is needed on another level besides sleep. However, we are able to override this need without immediate consequences, like an accident. Many people, by their own choice or involuntarily by the demands placed upon them by circumstances and others, are overworked. This state can go on for an extended period of time with health and psychological consequences slowly mounting.
While it can be hard to recognize what is happening and even harder to make changes, changes must be made or the problems will accumualte until a person collapses, has a nervous breakdown, resents those around them, throws themselves into oncoming traffic, etc..
It is better to voluntarily take steps that give you the rest you need, than wait for forced rest to overtake you. God's command to rest one day in seven seems a good place to start.