I have always associated Apollo with the mood and feelings. Mainly, I used to connect this with his music and poetry. However, today I realized how limited that idea was, because so many more facets of his being deal with mood changing and extreme feelings.
For instance, Apollo himself is falling in love all the time. But just as easily you can see him mad shooting people and animals alike. At one time he is playing the lyre, then he grabs his bow and, like the night, he comes and destroys. Just like day and night always follow one another.
It was light itself that reminded me of this. With the days shortening, we have fewer and fewer light hours here in Portugal where we are so used to light. Today my bedroom's light bulb went out and I was studying for ours with just the desk light. I got really depressed and started watching sad clips on youtube... Just because of the light! That's how strong Apollo is.
And I don't even need to mention the strong emotions that come with disease, death, health, growth, manhood, etc, etc, etc... All those associated with Apolo.
So, once again, I would like to contradict Freud and re-state that Apollo is not a god of meere cold reason - He is a god of cold reason and intense emotion. I guess one could say he is the god of the brain?