(1) Subject to this section, where, in respect of any period of incapacity for work, not caused by employment injury, an insured person is entitled to sickness benefit, he or she shall cease to be entitled to such sickness benefit for any subsequent period of incapacity for work, if he or she is appropriately certified by a registered medical practitioner to be an invalid; but is entitled to an invalidity pension or grant as the case may be, for so long as the invalidity continues.