Linda, So sorry things are bad. I have been on that neverending treeadmill of too much work and never time for a break too. One thing that helped me, was switching departments temporarily. I had a co-worker taking extended medical leave and they let me move into her position for the 4 weeks she was going to be off. It was still a lot of work, but having a different job provided the mental stimuation I needed and got me of the same treadmill I had been on for so long. Is your company big enough to make a departmental shift, even temporarily?
During the bad times, I definitely tried to leave the office during lunch. Even if I only took a 15 minute break and went outside, it helped. I always had a book to read on and if I could take a full hour, I often would go to a local park, read and eat my sandwich or take a walk.
Emailing friends, checking fb or TDK in a spare moment is also a nice mini break to remind you that your job is not your life. It is your means of having your life.
Hope things get better.