It happens... Sometimes the motivation is misplaced if you don't feel like you're getting out of it those things you want. Often, one can rekindle the energy by taking the training to a different level, thereby giving rise to questions and issues not encountered in day-to-day physical practice. Is there more than this? Why can so-and-so do things easier than I? What did Jones Shihan or Smith Sensei mean when they said that? And how did they learn? What are the core philosophies in Aikido? How did they come to be? If you can ask yourself questions and challenge yourself, emotionally, philosophically and physically, you will naturally be motivated to respond to those challenges. Doesn't work for everybody, but it might work for you.