Really interesting. It must take such discipline to collect this data for 3.5 years.
Trying to answer the question of "does work make me happy?" is much more complex than comparing happiness levels between work and non-work days - they are not independent. How much of your happiness of a non-work day is precisely because it is a day off? An imperfect analogy would be the feeling of enjoying a holiday but also being glad to be home at the end of it.