With regards to individuals and their levels of energy there are plenty of stuff that can affect them. There is certainly a condition known as constant fatigue syndrome, but this isn't the only real reason why many people feel like they are constantly tired and also have absolutely no energy.
Stress
It has been shown within a great number of studies that tension has a very major impact on a person's overall health. It impacts the immune system quite significantly because the body is so busy attempting to deal with the strain that it doesn't have time to protect against the virus and bacteria that are attacking it. Stress may also result in constant fatigue. This is because your body utilizes a lot of energy attempting to fight the stress and the effects of the strain and this takes a large amount of energy.
Health
One of the negative effects of being ill is your levels of energy will flag. The reason being the body is using just about everything that it has to fight the infection that is causing you to be ill. If you're fighting off a low grade infection that is not severe enough to really cause any kind of symptoms but is pervasive as well as long-lasting you may feel that you're suffering from constant fatigue while, in reality, you're actually using a lot of energy to fight from the poor quality an infection and stop it from becoming a proper full-blown disease.
Diet
Your body gets the nutrients and vitamins and minerals that it needs from the foods you eat. It utilizes these mineral and other nutrients to operate. You'll need particular vitamins and minerals and carbohydrates and other nutrition to keep your physique healthy. If you're not getting some of those nutrients then your body is not getting what it requires and it is not going to be operating at its optimum effectiveness. This can lead to a feeling of constant fatigue.
Constant fatigue syndrome
This is actually an extremely uncommon condition. Not much is known about this. Nobody knows what triggers this or how you can recover from it. We simply know that it exists. You have to meet particular criteria to be identified as having constant fatigue syndrome. The only thing to do in the case where you are identified as having constant fatigue syndrome would be to learn how to live with it and make the very best of the situation.
As you can see, there are a number of things that may cause a sense of constant fatigue. You have to go through them by a process of elimination before you conclude that you're struggling with constant fatigue syndrome. Most of these issues could be rectified while others have to just be waited out. The constant fatigue can generally be relieved at least a little by taking vitamin supplements and giving the body the help it needs to battle whatever is causing the constant fatigue. If it's indeed constant fatigue syndrome then you just have to learn how to live with the condition and the way to avoid aggravating it.