article_snippet.sent: It is usually caused by disease or head injury, but in rare cases can occur apparently spontaneously.
article_snippet.sent: In most cases, it is a temporary condition, lasting from a few seconds to a few hours.
article_snippet.sent: But in severe cases, it can last months or even years.
article_snippet.sent: The leading hypotheses are some form of epileptic event, a problem with blood circulation around, to or from the brain, or some kind of migraine-like phenomenon.