Right William, obviously you have a problem at work. You have given some scant information and other more informative stuff. To be honest I don't know if you are being harrassed or that management is just being assertive (there is a difference). However, here is my tuppence worth:-
1. Keep a record of what you described are "sly" comments. Just write the comments down soon after they have been uttered. It is important to record the exact words used and how you felt afterwards. Record in front of whom the comments were passed and on what date and even time if to hand.
2. I assume your employer has a Medical Officer. Some companies have a "doctor-to-doctor" system of reporting where requested. Perhaps you can discuss with the HR section if this system is applicable to you and get your answer in writing. Remember your company gets you to sign meeting attendance forms. Why not the other way round sometimes? If you have a doctor-to-doctor system use it and ask the company doctor to guarantee your privacy. They usually do.
3. Sick Leave History of employees is on the change at the moment. The Croke Park Agreement saw to that. But, there are no grounds for harrassment.
4. Involve your union and recommend the same action for your colleagues. If you are singled out for the alleged harrassment, then the problem is worse.
5. Keep a written record of each time you feel harrassed. Believe me you will gain some respect even from the most unworthy harrassers. I recommend you send an email to your private email address each time you feel you have been harrassed. Twenty pages of such records tell much more truths than twenty meetings or verbal argument and might give you the needed ammunition to fight back if necessary.
6. There are many people in management who fancy themselves as saviour-of-the-company. They seek out a reputation of getting the job done at all costs and they think they look good harrassing somebody. Some even thrive on this and make up their own rules for any sick leave situation. Get to know the sick leave work practice of your company. I am sure they will give it to you in writing. Read it, study it, get to know it; knowledge is power and you will soon know if you are being harrassed or not.
. . . and if you are being bullied . . . then get ready for your backlash . . . lots of bullying managers get sacked even in supermarket retail.