Learning how to play a new musical instrument is an example of procedural memory. Not much is known about the exact process of procedural memory storage in our brain. The most common method of brain research is fMRI scans, but these scans only tell us which brain regions are involved in memory storage, and only very little about the exact functional relationships.
What we do know is that during the day, memories (procedural or otherwise) are stored in a temporary, relatively unstable form and that these memories are greatly consolidated only during sleep.
What this means is that if you acquire new skills by practicing your instrument, the immediate improvement you'll notice is relatively small, but after a good long sleep the new memories will have consolidated and your skill is improved to a much greater extent. Therefore, even if you don't feel like you're improving right away, or you find it hard to remember new patterns, you have to wait until the next day to really judge whether or not you've made any progress. I'm not sure, however, whether this process extends beyond one night. It seems doubtful to me that taking several months off would be more effective than consistent practice in terms of memory consolidation.
Of course, another factor could be stress relief, which can have profound effects on your ability to think and focus. Switching from a stressful lifestyle to a more relaxed one could have significant effects on your skill acquisition process.