This is how it has been explained to me by my sponsor.
The pink cloud is similar to when you get a new hobby, job, house, partner etc...you are all buzzed up and enthusiastic for a period of time, the length of time varies from person to person. At some point it ends and things settle down...if you have done enough work on yourself to spark a dramatic personality change in this time then you will be able to cope...if you haven't you end up in some trouble, which may mean drinking/using again or worse.
This does make sense as i have seen it in the rooms in the short time i have been around, few have drunk/used again, one has become much more calm and serene, others share like they are split personality and rub their heads a lot. Only one of them has worked the steps, you can guess which one:-)