Understand always that the physical is a representation of the spiritual. One could say that all illness is derived from separation from source, the incomplete expression of the source of all love and truth, but how does this separation occur? Of course it occurs with the ego where there is a sense of a separate identity, a separateness that you identify with. And so the energy and the tension and the tiredness come about because of a lack of alignment. You might say that the ego expends a lot of energy holding on to certain kinds of self-concepts.
Human beings tend to see the ego as a psychological phenomena, but it is important to understand that the ego can use the physical body to control the being, just as the ego uses an addiction to help control the being. It is the psychological imprints or patterns, scripts, that help create the addictive behavior, and then the body becomes dependent on the drug or the food or the drink. But what of the people who are not addicted to drugs or food or drink, how can the ego assert itself?