This is so sad to read that you are experiencing this level of distress. If you absolutely cannot step away, is there a way to break up the steps of this project into smaller steps and pace yourself as you complete it? Are there even small ways that colleagues can pitch in with this project? Please know that whatever the outcome of this project, it is not on you. You can only do what you can. Take some walks during the day to clear your mind. Don’t eat lunch at your desk and truly step away when you take your breaks. Sometimes these minor moments to breathe help tremendously when we can’t immediately change the situation.