Depending on your attendance throughout the year, yes. If taking one day off helps you to refocus your mind and therefore be more motivated when you return to school then it's worth it. If you can, I’d spend some the day catching up on homework/revising so that you don’t feel like you're behind or wasted a day, but if you're feeling awful use the day to practise some self care and relax. Obviously don't make this a habit though!