I'm feeling sad, like the kind of sad I get on a Sunday, or when it's raining, or when I'm hungover.
But it's Monday, and I haven't been drinking and the weather's OK too.
If I see an old man on his own, it is likely to make me cry. If I see a mother kissing her baby, that will probably make me cry too.
Happy or sad, any emotion is guaranteed to have me in floods when I'm having one of these days.