Consider a machine that works day and night every single day. The machine can take care of itself but the machine is always busy in serving machines around it every day and every hour. Now, if it happens on regular basis, the energy that machine requires to actually function will come to an end, because even if the parts of it is getting the fuel it requires, it may not be able to process it. Why?

Because the machine requires the time to let the fuel do its job to every single part of it, so it can run smoothly again. Moreover, the machine may not only run smoothly but may also be able to function at its best because of the use of fuel and regained energy.

Now, replace the machine with the human body.

Even if we eat healthily, stay physically fit, and do everything that is considered healthy, when we don’t sleep, it's all useless. The human body will not be able to process it as staying awake requires energy. While we are awake, our brain consumes more energy, whatever in the body, than any other body part. Moreover, we won’t be able to function and may end up in heart stroke or heart failure if we don’t sleep ever.

So, when we sleep, the amount of energy required for our normal functioning of the body part is less as compared to during the day, and the brain uses this time to process the information such as bifurcating short term and long term memory.

We need our sleep for maintaining the body, and mind, social bonding, forming relationships, and other such aspects of one’s life