Determination and motivation isn't a feeling, it's a DECISION.
If you are procrastinating, going through a funk, or missing the spark you started with ... don't wait until you "feel like" doing something, because chances are good you will NEVER "feel like" doing it.
It just doesn't happen that way. The feeling comes after you make a conscious decision and begin taking action.
It is not possible to be 100% motivated and fired up every day. At least, not with the intensity you started with. To be successful, you have to know what your goal is and then DECIDE to never, ever give up.
Day by day, show up to your "weight loss job" and eventually your actions WILL pay off. No "feeling" necessary.
When pursuing your own health and wellness you can't let your feelings determine your actions -- you have to stay resolved to work on it every day no matter what. How do you stay resolved? Make a decision to be determined ... and watch that feeling magically appear.
Again ... if you've lost your original excitement, wishing for it to return is a losing strategy. If you're procrastinating getting started, waiting for motivation isn't going to work. You have to decide and go do it. Get back on the wagon and go.
Bonus: This is a philosophy you can apply to other aspects of your life and other responsibilities or things that are important to you but easy to put off (for example, your marriage, kids, etc).