The third Monday in January is known as Blue Monday. If you’re feeling down, you’re not alone. There’s a science behind your feelings. If you think about it, this day comes on the heels of the holiday season. That alone comes with highs and lows.

Brian Costello of Grounded Path Counseling is a licensed social worker, as well as a credentialed alcohol and substance abuse counselor. Costello says 5% of the U.S. population has seasonal affective disorder. Simply put, it’s low mood due to less sunlight. Costello says we have a biological response to the change in daylight length. We should be slowing down and resting, as animals do, but obviously life doesn't give us that luxury. Our serotonin levels, which control our mood, decrease, and melatonin, which makes us sleepy, increases.

If you are feeling down, Costello says there is a question you should ask yourself.

“Am I depressed or am I just tired? You know, do I just not have the same energy levels?" he said. "And is this a matter of expectation versus reality? Am I expecting myself to perform in the same way that I did? You know, three months ago, four months ago, when it was sunny and beautiful and everybody was happy?”

Costello says there are natural ways to increase serotonin. He suggests eating healthy — add whole foods, fish, cheese, nuts and turkey. He says those have tryptophan, which your body will convert into serotonin.

Vitamin D supplements and exercise will help you. That doesn’t mean hitting the gym.

Costello says it’s as easy as taking a walk. If none of this advice is helping, that’s when Costello says it’s time to talk to someone. But he says that doesn’t necessarily mean a therapist or counselor. Costello says talking to loved ones, such as a close friend, and getting your burdens off your chest goes a long way.