People often resort to getting a medical note from a doctor to present in front of their boss when they are planning to take a leave. Nowadays with so many sites and other sources cropping up where you can get them at cheap rates, things have been really easy for people. If your luck goes by with you, then your boss would not get a hint about the fakeness and you can just easily get along. But there are certain things which you need to keep in mind so that you can fake confidently in front of your boss.
First of all, do not fall for those free notes that some sites usually offer. If your boss keenly observes your fake doctors note that is downloaded from one of those sites, then he can easily catch you. Invest some money for a properly researched and developed one instead. Do not enter the office smiling the day after your leave day if you have made an excuse of sickness or death of somebody.
If you are out with some friends on your leave day, then do not post any pictures in any social media. Stay pale and uncomfortable in front of your boss. When asked, do not fumble while talking. You have to be ready beforehand with what you have to tell. Do not try to drink cold water at the office as you have apparently just recovered from illness.