A sudden, temporary loss of vision in one eye should be taken seriously, even if it improves on its own, as it can be a warning sign of reduced blood flow to the eye or brain, sometimes called a transient ischemic attack. Possible causes include blood pressure changes, migraine, or circulation problems, and it is especially important to check if you have risk factors like diabetes, high BP, or cholesterol. You should seek medical evaluation as soon as possible for an eye exam and basic tests, as early detection can help prevent serious problems like stroke. Do not ignore or delay care, and if the symptom happens again, lasts longer, or is associated with headache, weakness, or speech difficulty, seek emergency help immediately.