cause of near blackouts
One usually recovers quickly from fainting or near-fainting, but some people may have low blood pressures for up to 30 minutes and may feel groggy for the rest of the day. Causes. The most common cause of blackout episodes is a sudden reduction of blood flow to the brain, which is maybe due to: 1  sudden drop in blood pressure. 2  sudden change in heart rhythm. 3  postural hypotension (drop in blood pressure associated with sudden change in posture)