I have just written a very similar post. I find that one event throws me off and I just slip into 'not doing anything' very easily. I am reading these replies with interest! Remember - you are not alone!
I have been running on and off (more off) for a few years. The problem that I have is I will be fine for several weeks or months, running several times a week. But then one event will throw me off, for example a cold, a binge at the pub, a few cigarettes, missing a few runs on the trot. Then I don't get back on track and start it up again. I feel great when I'm on track and lousy when I'm not but just knowing that doesn't seem to help! Any ideas how I can break this cycle? In fact even I'm writing this now so I don't have to go out for a run!