Rarely is there a one-size-fits-all diagnosis in the world of mental illness, especially when it comes to depression. These types of ailments manifest differently from person to person. So, how are you supposed to know if you suffer from depression or if you’re just in a really bad mood? The brain may be a complex mystery, but here’s what we do know.

You’re grumpy today. Over it. Kinda angry, kinda sad. We’ve all been in bad moods. Irritability can be brought on by external factors like a bad night’s sleep, vitamin D deficiencies, allergies, poor diet or PMS (and PMS’s nasty cousin, premenstrual dysphoric disorder, PMDD). Sometimes, you’re late to work because your cat threw up on your pants and then the bus was delayed, so of course you’re upset!

Other days, for no reason at all, you wake up on the wrong side of the bed and life is pure lemons, no lemonade. Maybe Mercury is in retrograde.

The biggest indicators you’re simply in a bad mood are if—ta da!—it goes away and—voilà!— you’re still able to give work presentations, pay attention in class, feed your dog, bathe your kids and accomplish everything in between. Tomorrow is better (heck, it’s fun, actually) and your rut was nothing a post-work jog couldn’t fix.

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When your bad mood becomes your status quo and feelings of worthlessness, sadness, guilt or disinterest greet you every morning in the mirror, it might not be just a bad mood anymore. It could be high-functioning depression, also known as dysthymia or persistent depressive disorder (PDD).

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