There will always be cyclical periods of mental prosperity and decline.
You can't, "Do what you don't want to do," at least not as I understand it. Want could mean tanha or intention. You can avoid tanha, but intention is always the basis for action. So, when you meditate, it is because you want to; it's your intention. When you don't meditate, you don't want to. You should ask yourself, "In that moment, WHY don't I want to meditate?" Maybe you have a good reason. If you aren't mindful and relaxed, meditation is a waste of time; your mind is trying to use the activity as a means of self-gratification, yet is unsatisfied and therefore seeks something else. For people who are asleep, they do not benefit from sitting down asleep instead of standing asleep. In the short-term, you get bored. In the long-term, you give the practice up. In the really, really long-term you might not even be a Buddhist anymore and that's not necessarily a bad thing.
If you have good intentions deep-down, though, it really doesn't matter what we say because in the long-term, things will work out. The periods of prosperity will become greater and the periods of decline will become less and less, until you don't need inspiration anymore.
The best things in life aren't things.