Boy how many times have I hit this rut, namely losing the energy and desire to train after a long period of dedicated and strenuous training. Sometimes our biggest passions drain us to the point where we want to step away and take a break from it all. It's largely unavoidable; without periodization of some sort (or even a hiatus from the gym altogether) burnout and loss of desire, not to mention the loss of the fun aspect, for training will surface, particularly as age begins to creep up.
I find that a 2-3 week break is best, and if you're antsy about taking that much time off from the gym, I'll point out two options:
(1) Start a project, such as building a deck, performing home expansion, reconditioning a bike/boat/auto, etc. in place of working out
or, if you must
(2) Hit the gym several days a week (or less) for brief low impact light weight or endurance workout, such as swimming for 20-30 min
In short focus on extended sleep, rest, family, reading, etc. Anything but the gym, primarily. And don't worry or become to phobic about missing gym time; whatever step you perceive you lost will quickly bounce back with interest, and after this layoff you'll be fresh and ready to go again before you know it.
Worked for me and kept me on track.