My first impulse is to say not to to worry about training for the century. I've rode several centuries, some of which I trained seriously for and some I just got on my bike and rode.

However, my idea of a century differs from most other folks. I generally ride solo and unsupported so time is not an issue which eliminates one facet of training. I also do long distance rides on my LWB recumbent so body conditioning around saddle time and core strength for upright riding position is not an issue either.

For you Yen, I imagine that you might benefit from limiting your rides to recreational for a spell and resume training in earnest again when and if the motivation returns. I believe that as long as your body is strong enough to sit the saddle and support yourself in a comfortable riding position, the 100 miles will just roll by.