Instability of Mood

I noticed that when I am in a good mood, namely when I have enthusiasm, I am likely to practice meditation and avoid unwholesome behaviours. When I am in a bad mood, with low enthusiasm, I almost always succumb to some kind of unwholesome behaviour. How would Buddhism go about remedying such emotional volatility? It doesn't seem like these moods are actually *caused*, but merely arise in a fluctuating way. Thank you.