Most of the people I know who've practiced for a while have gone through this, sometimes more than once. I went through a burnout period for a few months until the desire to train came back. For me I was just in the dojo too much. I'd go to classes 5-7 days a week in two different cities. My body and brain couldn't keep up and classes became a chore. When I started back I limited myself to two classes/week as student and I eventually added two as teacher. This seems to work out well for me and I actually progress more with a little less training time
It really is about balancing it with the rest of your life.
I would really recommend you pick up George Leonard's book Mastery. It talks about this type of thing. The highs, lows, and plateus associated with learning, what they signify and how to recognize them for what they are...
stages in the learning process. You can pick it up at Amazon
Hope you can stick it out.