Is the testament of a person who experiences intermittent insanity valid?

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If a person who experiences intermittent insanity (mania/madness) issues a testament during a period of insanity, it is invalid. However, if he issues the testament during a period of lucidity (sanity), it is valid. This is because he is treated as a rational person regarding legal accountability, obligations of worship, and the validity of his transactions and testaments when lucid.