Korean teachers rarely call in sick from work and so the same expectation is expected of NETs to do the same. Most teachers usually go into work and then leave work early if they are not feeling too well. But if you really don't feel well and can't make it to work, make sure to let your school know at least an hour before work. You should NOT text message or email your co-teacher when requesting for a sick day. You NEED TO CALL and talk to your co-teacher so that your co-teacher can do you the favor of letting your school know and assisting you in getting your sick day approved by the school.
As per the contract, NETs are entitled to eleven (11) total paid sick days. The first three (3) do not require a doctor's note, regardless of whether or not they are taken consecutively. The remainder will require a doctor's note, which is basically an official statement from the hospital stating the procedure that you had done, and should include any instructions for further convalescence. It should also be signed, dated and stamped with the hospital seal.
Any sick leave that exceeds 11 days will be considered unpaid sick days. Those days will be withheld from your paycheck on a pro-rated basis. Only the days that you were to be present at school and were unable to attend will be counted towards the withholding (school/national holidays do not count).
If you have to leave early due to sickness or must go to the hospital/doctor's during a regular school day, those should be counted as "early sick leave" (병조퇴). 8 hours of accumulated early sick leave will equal one sick day.
Please refer to article 15 of your contract for any more questions regarding sick leave.