"...Only when the first assistant hasn't decided to become an incubus of viral plague. "
Ever wonder how to tell when your sense of guilt is overdeveloped? If you're sick enough to end up spending the entire day in bed wishing someone would just smother you and give you the sweet sweet release of death but the whole time you just keep thinking about how you should be doing research and you've just lost an entire day of work because honestly are you really *that* sick, then you might have a problem...
Also, I find it interesting that my tradition of getting sick on holidays has continued even when I'm in a country that doesn't celebrate the holiday in question.