It was probably your tolerance changing and your body returning to a more 'natural' state. When I smoke for long stretches, I always know when it's time for a break because I become unmotivated and lazy. That's when I'll quit for a month or so to bring my tolerance down and get back to 'normal'. Just listen to your body, it'll let you know what it needs, what it doesn't, when it needs it, and when it doesn't.