In need of a mental health day

I'm thinking about taking a mental health day sometime soon. Long term subs get one day or so (it'd be great if we got 2) to be absent and I'm thinkin' I might take mine soon. I can't decide if I want it to be on a Monday or a Friday. Which one is better? I think by planning this one day off, I will make myself feel much better and be able to face the rest of the assignment in a better disposition....possibly.