If it's just one day, take a lazy day. If it happens a lot, make sure you start focusing on you. Make a day a week dedicated to your mental and physical health, take a nice bath, listen to some awesome music, read, do things to "spoil" you so you know your worth it. That will motivate you to do things that aren't for you, but still kinda are. It helps to care about other things too if you know you are already cared about. That's what I do at least, and several of my friends. Gets us back to the real world and helps is care.