I call them mental health days. Physical and mental health are both essential to personal well-being. If your supervisor blows up at this, they need to take a mental health day. Or week.
Time to get rid of the stigma that colds and flu are the only excuses to stay home. No one wants to work with someone in a shitty mood and having a day off to rest and recharge is absolutely necessary.
Oh yeah? Him and what army....o wait...