Sudden dark eyes, dizziness, and unsteadiness in standing may be caused by postural hypotension, inadequate blood supply to the brain, sudden increase in blood pressure, diarrhea, vomiting, etc., as follows: 1. caused by postural hypotension: suddenly standing up from a recumbent position can cause a transient drop in blood pressure, resulting in low perfusion to the brain and inadequate blood supply to the brain. 2. caused by inadequate blood supply to the brain: when there is inadequate blood supply to the cerebellar brainstem, the main manifestations are dizziness , unsteadiness in standing, balance disorder and ataxia. Insufficient blood supply to the brain may lead to weakness of the limbs and blackness in front of the eyes, etc. 3, caused by sudden increase in blood pressure: Sudden increase in blood pressure may cause vasospasm, which can lead to insufficient blood supply to the brain, and the patient may also experience the above symptoms, which are mainly treated by regulating blood pressure to make it stable and not high or low. 4, caused by diarrhea and vomiting: If the patient is elderly, a large amount of diarrhea and vomiting can cause Hypovolemia and low blood pressure, suddenly up may also occur cerebral blood supply deficiency, and the above symptoms.