Well, try to remind yourself that it's not permanent. Sometimes you work on things that bore you to tears, other times you work on things that are much more stimulating. There will be challenging problems to work on again in the future, I guarantee it. I would suggest unplugging from work/digital life and take part in other things that interest you that don't involve screens. Taking breaks to do other things in life will revitalize your mind and you will find motivation again. Also, you will discover that you aren't solely defined by your work.