“(5) In assessing the extent of a claimant’s capability to perform any activity listed in Schedule 2, it is a condition that the claimant’s incapability to perform the activity arises from— (a) a specific bodily disease or disablement; (b) a specific mental illness or disablement; or (c) as a direct result of treatment provided by a registered medical practitioner, for such a disease, illness or disablement.”