What if you got a prescription for a craft project instead of a mood stabilizer? Would you think your doctor is insane? Well, not that I'm suggesting this should be the new standard of care, but I certainly believe that making something with one's hands can dramatically improve mood. (I bet even the craftfails..they are good for a laugh, right?)
This article from the American Craft Council points to some academic research that shows the repetitive motions of knitting relax the part of our brain that control the flight or fight response. Other craft activities have been shown to light up the pleasure center. More simply, the act of making something can feel like progress in a time when you feel adrift.
So, if you are feeling down, it might not be the time to attempt a sweater if you are a new to knitting. Start small with something fun! Pick something that is in your crafty wheelhouse, or a friend can show you how to do.