Advance directives may be thought of as self-correcting. If the patient is conscious and able to make informed decisions, the agent does not have authority under the instrument. Section 5-602(e) provides that (unless other provided in the document) “an advance directive shall become effective when the declarant’s attending physician and a second physician certify in writing that the patient is incapable of making an informed decision.” The second physician is not required if the patient is unconscious or unable to communicate by any means. Section 5-602 also provides that advance directives shall be made part of the medical record upon the attending physician learning of its existence and suggests forms for such directives. See also 79 Op. Att’y Gen. Md. 218 (1994). An advance directive may be revoked at any time by the declarant by a signed and dated writing, by physical cancellation or destruction, by an oral statement to a health care provider, or by the execution of a subsequent directive. § 5-604.