First of all, don't ignore it. Ignoring is resisting and what you resist, persists. So, acknowledge it and let it pass. Don't let it have any power over you. Try and be okay in now; the only way to ever be happy.
And when I feel down or low, I just let myself feel it. And then when I feel a little better, I think about what I want and it just makes me happy. Instantly.
This works for me, maybe it will work for you too.
Good luck. 