Stomach bug used to be my go to reason. However, now i very rarely have days off sick. I am self-employed so if i dont work i dont get any £.
Also, i find that working actually helps me. The worst bit is getting out of bed, getting dressed and getting to work. Once i am there, it isn't so bad. And 99% of the time i am always glad i went.
Forcing myseelf to act cheerful and happy in front of people can actually work wonders!