Mental or physical disability of the Governor continuously for more than 6 months. Whenever for 6 months a Governor in office shall have been continuously unable to discharge the powers and duties of that office because of mental or physical disability such office shall be deemed vacant. Such vacancy shall be declared by the Supreme Judicial Court upon presentment to it of a joint resolution declaring the ground of the vacancy, adopted by a vote of 2/3 of the Senators and Representatives in convention, and upon notice, hearing before the court and a decision by a majority of the court that ground exists for declaring the office to be vacant.