Sometimes you come to a realization that what you do does not move you anymore. This should in no way make you drop what you are doing and fall into a despair. Simply step back, take a deep breath. Now look at what you are doing. Consider what impact it has on the outside world. Step into the shoes of another person, whom you are impacting. Your work must have real world value. Not just “one man show in your backyard woodshed”. With that knowledge, put back on your shoes.
Another point is that it pays to have a hobby, even a minor. It is very rewarding to switch to something you love doing after long hours of work. It should be totally different from your 8 hours that you spend daily working. The human mind works in strange ways. It likes a change of thought direction, visual input, and stimuli.
Finally, everything you do must have inspiration backing it. Not just a reward! Reward is something you get. Inspiration is that godly feeling that makes you do stuff without any reward :)