Owing to the COVID-19 pandemic and the associated post-COVID syndrome, the concept "fatigue" has gained significant importance. However, both the definition and the causes of fatigue differ depending on the disease pattern in question. Moreover, individuals who describe their symptoms in everyday clinical settings seem almost universally to use the terms tiredness, fatigue and exhaustion synonymously. In 2007, Olson described these three terms as being distinct states in her view, but that they can be placed in relation to each other on a continuum. Taking up this consideration, an overview of current research is provided. For this purpose, the published literature of the last 2 years was searched for the terms "tiredness", "fatigue" and "exhaustion". Some common diagnostic instruments can be found. However, the great variety of instruments used to capture the three terms is striking. Despite these different diagnostic and definition possibilities, different therapeutic measures can be derived for each of the three symptoms. It is crucial, especially with regard to further therapy, to separate the three terms tiredness, fatigue and exhaustion from each other and to consider each of them separately on the common continuum. This is the only way to establish both an accurate diagnosis and the successful individual therapy that goes along with it., (© The Author(s), under exclusive licence to Springer Medizin Verlag GmbH, ein Teil von Springer Nature 2022.)