Depression. Anxiety. Pain. Stress. Fatigue. Below, I've plotted the past year’s worth of daily Google search interest in these five terms, which I've aggregated into a index of misery.

Higher numbers indicate greater search interest in the five terms, which all had a lot of search volume with reliable data.

The searches rise in the spring and fall, ebb during the summer months, and drop sharply during holidays. Christmas is the least miserable day of the year, with Christmas Eve and New Year’s Day not far behind (numbers for December of this year are projections based on last year's figures). A seemingly random Wednesday in late April may be the worst day of the year.

Peaks and valleys in the raw numbers -- the light blue line -- reflect the rhythm of the workweek. People are more miserable on weekdays, less so on weekends. Averaging out each day over the past year, Tuesday and Wednesday are tied for the most miserable day of the week, with Monday and Thursday not far behind.

Among the five search terms comprising the index, “depression” and “stress” show the most day-to-day variation. Pain and anxiety peak on Mondays, stress and depression on Tuesdays, and fatigue on Wednesday. Searches for all terms drop sharply going into the weekend and then edge back upward on Sunday.

On one hand, the daily ebb and flow is not surprising -- we like weekends a lot better than we like work days. On the other hand, these numbers suggest that people literally hurt more on Mondays, which is pretty astonishing.

It's also notable, looking at the top trend chart, that the gap between weekends and week days shrinks in the summer months: those peaks and valleys are a lot closer to each other in July than they are in March and April.

If we are what we Google, what do these trends tell us about ourselves? I posed this question to Dr. Elinore McCance-Katz, who is a psychiatrist and Chief Medical Officer at the Substance Abuse and Mental Health Services Administration, which is an agency within HHS. Looking at the big annual picture, she said that seasonal blues probably plays some role here.

"It's been shown pretty clearly that as daylight decreases, starting in the fall, people will have more feelings of depression and anxiety. If they are feeling depression and anxiety they will report stress," she told me. This would explain the uptick in misery-related searches from late summer through fall.

But there's something else going on too.

If you look at the annual trend in searches for "seasonal affective disorder," for instance, you'll find that these peak about when you'd expect them too -- in December and January. But the broader terms like "depression," "anxiety," and "stress," all show a pronounced dip in December, which is reflected in the Index chart above.

One explanation? Holiday-induced euphoria. At the daily level, Thanksgiving, Christmas Eve, Christmas day, and New Year's day are all among the year's least-miserable days. We hear a lot about holiday-related stress, and the numbers certainly do show some high-misery days in November and December. While I wouldn't go so far as to say the holidays are the most wonderful time of the year, there's pretty good evidence here that they're the least-miserable.

But what's happening in the Spring months? This is more of a mystery: you'd expect people to get happier and less miserable as the days grow longer and temperatures get warmer. But according to these Google searches, misery peaks in March, and a random Wednesday in April appears to be the most miserable day of the year.

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.

The good news, according to Dr. McCance-Katz, is that these feelings of malaise are easily treatable, and that if you experience them you're far from alone. SAMHSA's latest numbers show that 43 million American adults -- nearly one-in-five -- experienced some form of mental illness in the past year. Many of these disorders are easy to treat with medication or therapy.

Some notes on the data

There are of course limitations to how much we can say about a society's mental state based solely on search figures. For instance, Google users are a non-representative subset, albeit a large one, of the broader population. Moreover, there are plenty of reasons why a person would search for, say, "depression" when they're not actually depressed themselves: depression searches spiked in late August this year around the death of Robin Williams.

On the other hand, it's completely reasonable to posit that these searches do reflect broader public health trends. Google data is used to track influenza outbreaks, for instance, although doing so is not without its methodological pitfalls.

More to the point, the daily search volume for the five terms I used to create the index followed very regular patterns, which are reflected in the charts above. Aside from the burst in interest in depression in August mentioned above, there were no large unexpected spikes in the data that had to be accounted for -- this suggests that underlying social phenomena are driving these numbers.