Blackout is a condition characterized by the temporary loss of consciousness and muscle strength, usually caused by a lack of oxygen supply to the brain. It is also known as fainting, passing out and syncope. Pre-warning symptoms of a blackout include lightheadedness, dizziness, blurred vision, a feeling of weakness and palpitations. Sometimes, chest pain and shortness of breath may be experienced too.
Common causes of a blackout include low blood pressure, heart arrhythmias, heart valve problems, heart attack, anaemia, dehydration, low blood sugar, certain medications and neurological conditions.
Often black-outs can be preceded by symptoms of dizziness. Here you can read more about dizziness, as often the investigations and treatments are the same.