I have to agree that work is work regardless of whether one likes it or not. Work and leisure are essential. Personally I work in sprints where I work like crazy and then make sure to take time off to recover. I also use recovery time for reflection, both structured and unstructured. I would class the structured reflection as work but naturally my mind processes automatically in down time also when I'm out riding my bike or whatever. This is where all the best ideas and plans come from.

Take the analogy of an athlete. Any athlete knows that recovery is an important part of training. Too much work and they over train. This can be applied to any area of life but is usually called burn out in business. Burn out happens regardless of how much one enjoys the work.