Some people get tired or even more than tired and are thereby suffering varying degrees of fatigue, on a near constant basis, of which, undoubtedly, some of these people are suffering from something of a biological or of a mental origin which is creating or contributing to that debilitating condition. Yet, not everyone that is exhausted or fatigued, actually is genuinely in that condition, per an explainable or plausible medical condition. In other words, for some people, even unwittingly, their feelings of fatigue or exhaustion are part and parcel of something that they believe has a biological origin, or something involving some sort of brain malfunction or chemical imbalance, or in any event that has a reasonable explanation, but as in many things, that is not always the case. Additionally, there is also all those people that logically become exhausted or fatigued when they are overworked, stressed out, or sleeping poorly.
Then there are those other situations, in which people seem to be absolutely exhausted, but somehow, when an unexpected phone call comes in, or an unexpected visitor comes by, or there is some sort of outstanding news, suddenly those that appeared to have no energy, become quite exhilarated and alert. This reaction primarily occurs because life often consists of a lot of ordinary moments, in which living in a same day in and same day out routine has a tendency to become exceedingly dull and enervating, so then when something unexpected occurs, and especially when that unexpected event is something that is highly desirable, people awaken sharply from their slumber, and that dullness, so exhibited by their fatigue and exhaustion, simply vanishes away.
Yet, there are also those other situations in which people express exhaustion and fatigue, but there doesn't appear to be a valid reason why this is so; of which these situations often have a lot to do with a given person's position within a family dynamic or something similar, in which those that are expressing fatigue, are doing so not really because they are actually physically fatigued, but rather as a way to fight back against their perceived powerlessness against whomever or whatever seems to be bossing them around. In other words, for instance, those that are in subservient positions, in which they know for a certainty that they will never have the upper hand, find that the only conceivable way that they can fight back, is to feign that they are too weak, and too tried, to do any more than what they are currently doing, and thereby do less of what they do not wish to do.
So what we find then, is that in this world, not everything always appears as it really is, for people react to the world as it is perceived by them -- the injustice of it, or the unfairness of such; all of which can thereby be manifested through the emotions so displayed. We are therefore not just what we feel that we are in our body and our mind, but we reflect also in our mannerisms our take upon how we see the world and our situation. Therefore, those that are in what they consider to be helpless, hopeless, or downtrodden positions, may well find themselves feeling exhausted and quite fatigued, because that is their preferred way of dealing with being oppressed.