The Hedonic Treadmill

I worry a little about the hedonic treadmill. Things have been going great recently, but what if my baseline happiness is actually far lower than I am at currently, and a decline in my wellbeing is inevitable? Today I don’t feel as great as I have for much of the last month, even with very little reason - everything around me is still wonderful. Hopefully it is ‘just one of those days’ and not my mood regressing towards the mean.