In Germany employees have financial security when they fall ill. Your employer will continue to pay your wage for up to six weeks; some collective wage agreements have even longer periods. After that you are entitled to sickness benefits (sick pay), which you receive from the AOK: The sick pay amounts to 70 percent of the regular gross earnings, however at most 90 percent of the net earnings received up until that time. You can receive this payment for the same illness for a maximum of one and a half years (78 weeks).
The employer must be informed promptly if an employee cannot go to work because of an illness. What the deadlines are exactly and whom you have to contact differs from company to company. To be on the safe side it is best you ask you employer for this information. Insofar as the illness lasts longer than three days, you shall regardless of the circumstances, require a medical attest that is issued by a medical physician, irrespective of whether you have a special arrangement with your employer. You receive two copies: One without a diagnosis, which is for your employer; one with a diagnosis that you hand in to your AOK. Please bear in mind that you must hand in the sick note to your AOK and your employer as soon as possible.