Doing mental or physical work while exhausted may harm your health, according to a study from University of Alabama at Birmingham and published in International Journal of Psychophysiology.

In the study, fatigued people had bigger spikes in blood pressure compared to well–rested people while doing a memorization test. When fatigued people regard a task as worthwhile and achievable, they increase their effort to compensate for their diminished capability. As a result, the blood pressure of a tired person increases and remains elevated until the task is completed or the person gives up. In this study, the researchers told 80 volunteers that they could win a modest prize by memorizing 2 to 6 nonsense trigrams (meaningless, three–letter sequences) within two minutes. Compared to volunteers with low levels of fatigue, those with moderate fatigue had stronger blood pressure while doing the two–trigram memorization task.