If your sickness extends over an Off Day, the company still considers that day as being sick, unlike other company personel who fall sick on the weekend in the Golden Palace, whereby it does not count as a sick day. ie. no recovery for being sick on their off days.
If you call in sick on a Rest Day, prior the next days flight, the company considers the Rest Day as another sick day, in spite of the fact it is NOT a Duty Day. Therefore, you would be silly to call in prior to midnight before any next days Duty.
You will not be marked absent for calling in sick, less than 4 hours prior to duty, provided you state that you woke up.... SICK.... and notified them promptly.
Contrary to the lies from the management types posting here on Pprune, sickness rates are at an all-time high. Go peruse 10 rosters at random and this fact becomes blatantly obvious.