A black eye when standing up suddenly while sitting is likely to be caused by postural hypotension. Postural hypotension refers to a drop in blood pressure of more than 20mmHg when the position is suddenly changed, such as when the sitting position or the prone position is suddenly changed to the standing position, compared with the sitting position or the prone position. The drop in blood pressure causes a temporary lack of blood supply to the brain, which leads to black eyes, and some patients may even experience fainting and fall. For patients with postural hypotension, it is necessary not to move too fast when changing positions, but to slow down in general. Patients with severe postural hypotension can also wear compression stockings or pants to prevent it. In patients with cardiovascular disease, diabetes or anemia, it is important to aggressively treat the underlying disease.