Everyone needs some time off once in a while.
According to a study at the University Of Texas, Wednesday is the best day to take off.
Taking Wednesday off helps complete a pattern. Since weekends are 2 days, you would have 2 days off, work 2 days, have your day off then work Thursday and Friday. And have another 2 days off the following weekend. The day off helps at the beginning of the week as well because it's not another 5 day work week and that SHOULD reduce some stress.
Some people also say that taking Wednesday off is ideal if you want to do things because there might be fewer crowds at place.
There's much more on this here.
Photo credit: 10'000 Hours