Lucid Interval

A period of mental clearness enjoyed by an insane person, during which he is capable of performing an act which will be binding in law. Not a restoration to reason, but a restoration so far as to be able, beyond doubt, to comprehend and do the act, with such reason, memory, and judgment as to make it a legal act. An act done in a lucid interval by one who has been found to be a lunatic is binding on him, but the proof of the lucid interval must be clear. The expression once meant respite, intermission, cessation, relaxation.

See Lunatic.