One of the most powerful attributes a conscious human being has is his will. In the upper levels of mysticism, we consider it “divine” and “free”. There are influential forces in our everyday life, but ultimately what you choose to do is based on your divine-free-will.
Words are also incredibly powerful. Be it pure coincidence, the subconscious mind or it having some ancient etymological relationship, all words can be “spelled”and “Spells” use words. What comes out of your mouth is literally manifesting into vibration from the ethereal to the elemental world.
If you are feeling down or in a negative way, simply choose to decree or say the way you want to feel. Say: “Right here and right now, I choose with my divine-free-will to be healthy and happy”. You don’t need to believe it. Actually, just say and don’t expect anything out of it. Just say it because you can and because you have the power to. Say other good things as well in that context, at the very least it will momentarily replace a negative murmur. I can assure you though, that if you pay attention, and look back a few hours or days later you will notice that certain things manifested to heed those commands. This will also teach you to be very careful of what you say in those moments of mindless utterance.