This has been dealt with quite a few times here (search burnout) and recently too:<p><a href="https://news.ycombinator.com/item?id=14320392" rel="nofollow">https://news.ycombinator.com/item?id=14320392</a><p>Check the comments.
Do you take time to rest every so often? I used to work 7 days a week on my SaaS but now I make sure to take some time once a week to have a day off, to relax, to mediate, have drinks, see friends, etc. No code for a whole day.