You have to know that the weekend is coming to an end. You have to embrace the spirit of carpe diem and realize that you have a limited amount of time to spend. The key is to be serious about the goals and the items that you want to accomplish on the weekend.
If your goal is to relax before Monday, then that should be your goal. The process of meeting goals will take the stress out of the weekend. You want to be able to say that you accomplished something, this will take the fear out of Monday.