You have probably wondered before why you are so tired. There is no one standard answer to this question. In fact, fatigue symptoms can be caused by many things. Sometimes there is one obvious cause for fatigue, for example if you have been exercising a lot or sleeping little. However, it is usually caused by a combination of several factors. Often it is because you do more than your body can handle. Diseases like Pfeiffer's disease, the flu, corona or diabetes can also cause you to be overtired. If you are very tense or stressed, suffer from depression or have an unhealthy lifestyle, this can also cause you to feel tired.