Chocolate will increase your serotonin level. Works like an SSRI and it's so much more satisfying than swallowing a pill! (I'm not discounting antidepressants. When I'm PMSing I thank all the scientists who created prozac. But a little self-care doesnt hurt, either)

FYI- in the Harry Potter books, Harry was given chocolate when he faced dementors. The dementors are depression personified. When you come in contact with one you feel like you will never be cheerful again. So what is the cure? Chocolate! There is some real science in those books.