Why Am I Always Tired - Why People Get Tired?

Why am I always tired?

Fatigue can be considered a sort of intoxication. 
When the muscles of our body work, lactic acid is created.
If we remove the acid from the tired muscles, they will be able to work again.

During the day, we are, we are “poisoning” ourselves with lactic acid. 
Also there are other substances which are produced during muscle work, and these substances are called poisons fatigue. They are carried by the blood throughout the body, so we feel tired not just in the muscles, but also in the entire body, especially the brain.
Scientific experiments related to fatigue are showing some interesting results. 
If a dog gets tired to exhaustion and sleep, and then its blood is injected into another dog, that dog will also immediately become tired and fall asleep to.
If, on the contrary, a tired dog receives a blood transfusion from rested, alert dog, this dog will immediately wake up and will not feel tired.
Fatigue is not only a chemical process, but also a biological.
We can’t simply "remove" tiredness, because the cells need rest, to rebuild and be able to work again. Therefore, fatigue is a signal which indicates that the body needs rest to rejuvenate the body's energy.
However, there is something of particular interest in the rest.
Someone who has worked hard for hours at a desk will not want to lie down when he gets tired.

He will want to walk! 
Or when kids get tired from school, they don’t lie down to rest, but they run out to play.
This can be explained as follows:
If only a part of the body is tired, such as the brain, eyes, hands or feet, the best way to refresh that part of the body, is to activate other parts of the body.
Movement enhances breathing, blood circulation and glandular activity, and pollutants leave the tired parts.
But if someone is exhausted, the best rest is a dream.