Someone placing excessive demands on your time on monday needs to be told no in no uncertain terms. Stand up for yourself, and get your boss to do the same if necessary. Your higher-ups are there to support you, but don't be surprised if you and your supervisor have a difference of opinion on tuesday or wednesday. You're entitled to your beliefs, but theirs hold more weight (you can always say "i told you so"). A coworker comes to your aid in a key situation at the end of the workweek. Make a mental note to repay them later. Avoid working this weekend if possible. You deserve a break!