The teacher is permitted up to three to six days of paid sick leave when the teacher is unable to attend class due to illness. He or she is required to notify the employer and submit an accompanying proof of illness from a physician.
Since your co-workers are automatically the often-unwilling recipients of your classes if you call in sick, it's not a good idea to do so unless you really are sick. Hangovers, or just having a bad day, won't be acceptable excuses for missing teaching to either coworkers or management.
Legally, for any sick day taken, your employer can deduct a day's salary unless you present an official note from a doctor. In practice, most employers don't ask for this note unless someone has been absent for more than one day or has a history of one-day illnesses.