Tired all the time

Feeling tired is normal human experience and can occur either because of a lack of physical activity or physical energy or lack of psychological motivation to act.
There is a very powerfull interaction between these two broad factors "Tired all the time" is a relative change in any or all these factor.
Physical energy is the capacity of the tissue of the body to engage in their normal metabolic activity to function normally.
Tissue require oxygen and fuel to provide energy and stimulus of wild variety of chemical messenger to drive metabolism.
Some tissue also require period of recuperation in a different state to maintain their function (most obsivioly the brain which head sleep) psychological motivation is complex and venes naturally but is affected by psychological condition such as depression.
The metabolism of cells may be depressed by received too little oxygen. Oxygen enter the body via the lung and it transported.
To tissue attached to hemoglobin in the blood stream poor oxygen supply function. Insufficient functioning hemoglobin or in sufficient blood flow.
Patient now can not get air in too the lung because of airway or muscle problems or who cannot get oxygen from the lung into the blood will tired easily (COPD) or disease affected in the interstitial tissue in the lung or blood flow through it.
Oxygen transport in the blood required normal level of hemoglobin-low hemoglobin or anaemia is common and often undetected. Sufferers often feel tired and have low exercise tolerance making hemoglobin required iron and B12 if there are deficient them there will be anameia as will happen if the processes which make red blood cells are disturbed alternatively hemoglobin may be present but not functioning as happen in low level carbon monoxide poisoning cells also need glucose if the concentration of the glucose in the blood is low or more commonly glucose can not enter cells then metabolism will be compromised this litter happen in diabetes whose will not reach the oxygen in adequate a mounts this commonly happened in heart failure where poor general perfusion can leave patient feeling tired.