Being stressed out isn't a good thing at all because you won't be as productive either with your playing the piano. Take a break for a few days and do something different for yourself.
Go out for a walk or a drive, get out of town into the country. Quit beating yourself up over
the little things as you are learning a piece because music has a way of working itself into
your playing anyhow.
Just be diligent in your practicing, but over do. Practice 15 minutes at a time and then take a break, a little walk, or eat something and the can help relieve the stress also.
The mind is an interesting thing and we can control it by our actions, in limiting ourselves from not over extending ourselves.
I don't know if you are a professional pianist, or a student, in which you haven't indicated in your post. However, just don't push yourself so that you get stressed out because a piece isn't coming along as you would like it. Again, hopefully, things will ease up for you so that you can enjoy playing the pieces and not be as stressed out.
best wishes,
go12_3