My wife is a Spiritual Life Coach (among other things) and has long been tracking the ebbs and flows of her clients. Whether we believe in such things as "other" forces, she had hard numerical evidence that there are "ebbs and flows" in when her clients seek help, and when they don't.
In other words, in a perfectly neutral universe, she should get client calls at a pretty constant rate. She does not. And she just walked through my office and declared "I swear, it seems like everyone is ready to jump off a tall building, this weekend!"
Not saying that "means" anything, but I've noticed that I tend to go through "cycles" (about every six weeks or so) where my creativity ebbs and flows, as well.
My thought is that "little tiny stuff" affects us. We may not have the science to "measure" it in 2017, but maybe in 2117 we will... and it will just be yet another natural phenomenon, like tides, gravity and such.
I have noticed this cyclical nature also within myself but it has felt a little different. I took the day off and had brunch with friends and spent the day walking around outside with the family. After a half decent sleep, I think it has helped somewhat.
It is interesting how many things can affect a mood or a thought pattern. I am sure that one day there will be some discoveries that unlock some of this stuff.