It's easy to over-analyze this stuff, but if you don't feel like riding, it's probably not a bad idea to quickly check in with yourself and think about why you feel that way. Could be your ride has gotten stale, could be there's something unpleasant happening on your rides, could be you've got a nagging injury, could be you're coming down with a cold...it's never a bad idea to listen to what you're feeling, even if you don't always do what your feeling seems to want you to do.