Relapses do happen, but I think calling it relapse is too strong a word. Any progress is a trend encompassing ups and down. Another possibility is what sportmen and women call "choking".
Choking is well explained in Malcolm Gladwell's new book "What the dog saw", in the chapter entitled "Why some people choke and others panic". Basically, if you care very much about success, then something happens to trigger an awareness of your stereotype of success (say a comment, or a look) you start to over-think about an action which is normally automatic, resulting in not being able to do it automatically.
He gives two examples: one is Jana Novotna in the 1993 Wimbledon final against Steffi Graf. The other is Greg Norman against Nick Faldo in the 1996 Masters. In both case Jan and Greg were ahead; by the nature of the event, they cared very much about the outcome; they were faced with a stereotype for success; something triggered their awareness of this and of the task ahead of them: they both began to think about this; it was noticeable that their actions became uncoordinated instead of fluid: and they both lost the match. Remarkably, both victors commiserated with the loser, showing that they were personally familiar with what had happened.
It has relevance to what we do: we care very much about the necessity to go, we are faced with stereotypes of success i.e. others going with no effort; this contrast with oneself makes us aware of it, we start to think and over think about it; the result is that we consciously try to make ourselves go, instead of going on automatic pilot and letting it happen naturally.
Hence the need to reverse these components i.e.
1. the importance of not caring if you go or not
2. accepting that we are slow at it, and that we are not in competition with others
3. to control our negative thinking i.e. the Boo Monster
4. and so to get to a point where the whole process is routine and takes place automatically.
Hope that helps