May Moods

Dr. McCance-Katz points out that researchers have discovered greater incidence of depression and anxiety in the spring months, too. As it turns out, lengthening daylight may discombobulate people's chemical regulatory system. "There are these different neurotransmitters that have been implicated in mood disorders," she says. "It could be that people also have imbalances in serotonin, in melatonin, that are affected by day length and can also affect mood."

Mental health experts consistently find that suicides peak in the Spring, for reasons that aren't fully clear. The uptick in misery reflected in the Index above likely reflects some of the drivers of this phenomenon.
https://www.washingtonpost.com/news/wonk/wp/2014/12/03/the-google-misery-index-the-times-of-year-were-most-depressed-anxious-and-stressed/