Training is just as much about motivation than the effort - and in my opinion one directly affects the other. It is easy to see the difference down at the Dojo between someone who is there to fulfill some personal commitment and someone who is there to simply...be there. Training is about being better at a particular thing, which includes motivating ones self.
Many people get exposed to, through social media like Facebook and Twitter, the motivational pictures and sayings. It is all good of course, but motivation and theory are just like philosophy. Useless unless it is applied. Pointless if it stays in your head. You must but it in your hands, feet and heart and actually go ahead and do it.
The fact is, sometimes we all experience lack of motivation. A slump that feels like we cannot break out of it, or perhaps we fall into 'Tomorrow Syndrome'.
"The diet starts tomorrow"
"I will do that tomorrow"
When it comes to training, effort is always rewarded. Exercise increases motivation, mood and wellbeing in general. A half-arsed attempt at a Kata may not do the 'Spirit of Budo' justice, but a half effort is still an effort, and it might just be the thing that helps to motivate you to try harder and train more.
When you are feeling this way about your training, don't stop training! Keep training. Keep doing your practice, your exercises. Don't wait for a magic moment to change your mind/feeling, however, but know that in making the effort you are bettering yourself.
Share your feelings of de-motivation with your peers, family, friends and more importantly your Sempai. Listen to their own experiences and realise that being de-motivated is, itself, a part of your training journey.