It's the Tuesday after Labor Day, and you're probably very bummed to be at work. You'd think after a long weekend of beaching, or boozing, or vegging, or all of the above you'd feel refreshed, ready for the short week ahead. But, no: Today stinks. Don't worry, though: according to science, your depression makes perfect sense. You have what The Wall Street Journal's Melinda Beck describes as "Post Vacation Syndrome, characterized by a combination of irritability, anxiety, lack of motivation, difficulty concentrating, and a feeling of emptiness that lasts up to a few weeks after returning to work." This diagnosis might lift your spirits, in a few weeks you'll pull yourself out of the doldrums, back to normal. But, don't get too excited, because unfortunately it looks like there's an unpleasant mood for every season.

Obviously Post-Vacation Syndrome applies to any and all vacations, meaning you should plan on a slump not only after any long weekend, but after longer breaks, too. You might think the tease of a three-day weekend has something to do with your mood: Maybe the long Labor Day weekend wasn't enough? Nope. Longer vacations don't do squat, reports MSNBC. "Interestingly, a longer trip will not prolong your post-holiday happiness. Research has not found that the amount of time you spend on vacation has a significant effect on your spirits afterward." Remember Christmas week and spring break? Not going to make you any happier. 

Yet, it's true, there is something particularly sad about the end of Labor Day weekend: It means no more summer. And the changing season affects your mood. As summer fades, the days grow shorter, meaning less daylight, which as Beck points out, explains some of your sadness. "The waning daylight is already reducing the availability from the sun of vitamin D, a building-block of serotonin, the neurotransmitter linked to depression." But it's only getting worse. The days are getting shorter and with the coldest, shortest days you might suffer seasonal affective disorder.  "Your symptoms start in the fall and may continue into the winter months, sapping your energy and making you feel moody," explains the Mayo Clinic.

So maybe you're looking forward to another summer, hoping it will bring bliss back to your life. Sadly, summer, too, makes you cranky: the heat gets to people. "Clearly, hot temperatures produce increases in aggressive motives and tendencies," a Psychological Bulletin overview found. That really only leaves spring, but with few federal holidays in that season, you'll probably opt for a long vacation and dive right back into your depression.