Whenever I get irritable, it is because I am a bit hungry. So, when I am easy to irritate and start to be annoyed, my girlfriend tends to, of course for a joke, say that she has to feed me. But, seriously, when I am fed, I am no longer irritable.
Whenever I get depressed, it is because I am a bit short of sleep. So when I am in such a depression that I cannot concentrate on my study any longer, I make it a rule to go to bed. And I have got enough sleep, I am far from depressed.
When your mood is easily influenced by your physical sates, it has its advantage and disadvantage. The good point of having such a mood is that by making use of that vulnarability you can control your mood. Satisfaction of my physical needs always helps me recover from the mental mess. The bad point is that you feel like your mind is somewhat devalued. The realization that my mood is just a dependent variable which is a function of the independent variable, my body state, stripped it of the profundity that had disposed me to make much of it.