AIC 06/16
“1.1 This circular serves to remind every holder of a medical certificate issued under Article 19 or 20 of the Air Navigation (Hong Kong) Order 1995 that he/she is not entitled to act as a member of the flight crew of an aircraft registered in Hong Kong if he/she knows or reasonably suspects that his/her physical, mental, emotional, physiological (such as fatigue) or social condition renders him/her temporarily or permanently unfit to perform such functions or to act in such capacity.”
UNFIT FOR DUTY does not mean SICKNESS, there are many other factors.
If you report UNFIT and do not provide a Doctors note, then you are UNFIT for reasons other than sickness. This by definition is not dealt with by the Sickness Policy or the COS, but can be monitored by the AMP.
DO NOT SELF CERTIFY AS SICK, ONLY AS UNFIT FOR DUTY.
If they wish for you to see a company appointed medical specialist later then you will have to comply as part of the COS.