"I don't feel like it today."  

That statement there is a two-edge sword. 

 On the one hand it's important to listen to your body and take care of your mental health.  On the the other hand, if you find yourself not "feeling like it" while you've also got goals you want to achieve...  

You're only holding your self back. 

There comes a point where "I don't feel like it" becomes an excuse for laziness.