You must inform your employer if you are unable to work due to sickness. You may be able to get sick pay or other benefits. Your employer may have rules about what to do if you cannot come to work because you are sick. They can, for example, insist that you tell them you are sick on the first day that you cannot go into work. Your employer must let you know what these rules are in advance. If you don’t keep to the rules, you will be breaking the terms of your employment contract.