A conversation I had a few years ago with a flight "manager" went something like this?

Them: I see that you called in sick. Do you realize that you called in sick 5 times in the last 365 days?
Me: Yes
Them: Are you able to furnish a doctor's note if I request one from you?
Me: No
Them: Why not?
Me: Because I did not go to the doctor.
(Long silence)
Me: Anything else I can help you with?
Them: No
Me: Thank you for calling.

Sick time is negotiated time off, nothing more. You do not leave your rights (Privacy, HIPAA, etc.) at the door when they hire you here. The instant I ever get the slightest tinge of overbearing attitude about sick time usage from one of the Pilot Pushers I will call the FSDO/POI without hesitation. I am sure it would not be the first time the company's representatives were accused of trying to make someone think twice about calling in sick, thereby violating FAR §61.53. You are the only person that can evaluate your physical and mental fitness to do the job.

As a refresher only...

§ 61.53 Prohibition on operations during medical deficiency.

(a) Operations that require a medical certificate. Except as provided for in paragraph (b) of this section, no person who holds a medical certificate issued under part 67 of this chapter may act as pilot in command, or in any other capacity as a required pilot flight crewmember, while that person:

(1) Knows or has reason to know of any medical condition that would make the person unable to meet the requirements for the medical certificate necessary for the pilot operation; or

(2) Is taking medication or receiving other treatment for a medical condition that results in the person being unable to meet the requirements for the medical certificate necessary for the pilot operation.