How to give yourself a mental break (and not feel guilty about it)

Plan and schedule breaks into your daily schedule.
Let your brain know that within a relatively short amount of time, you will have a clear break to check social media, walk around, respond to texts, or do whatever nonwork habit you want.

Consider taking a real lunch break. 

Eat or do whatever you need to do to process and calm your internal self, so that you will be able to go back to work and focus on getting things done.

Set a time when you are done with work for the day, and give yourself permission to really disconnect in the evening.
While working at home, you may become unclear when your work stops and your personal time begins and you may feel guilty for relaxing.