It's quite odd how we shift from one mood to the other, sometimes instantaneously, some other over a larger period of time. Perhaps even more intriguing are the triggers, the said reasons, of that mood shift, which we don't always realise they have been acting on us, or that they have been gathering into a swarm to for a good reason for the shift. It is always much easier to be neither sad nor happy, in a somewhat a neutral state with a tiny bit of flavour of either, since it requires the least amount of concentration and emotional self-evaluation. Yet that state I find to be rather fragile, and easily overturned, often without much power of protest, into either sadness or happiness. Note that here I use happiness and sadness as categories of emotions.
Personally, I believe there is no real value to emotions, with value understood as a characteristic of an adequately constructed entity, on solid foundations and for good reasons, since they are merely the psycho-physical manifestation of subjectivity. The reasons for our sadness or happiness could be a largely misinterpreted situation, a semantic error, or just a surge of a certain kind of neurotransmitter, which do gives us real experiences, but the nature of that experience lies in the space of our own imagination, without any real concrete existence, thus implying that we are making ourselves, even if involuntarily, feel a certain way, but without a adequate reason. This goes to say that emotions are not either based on solid foundations, nor are constructed for good reasons, therefore they have no real value.
This gives way to the sinuous nature of the shift of moods, from one extreme to the other, first because the previous mood was not adequately constructed, thus flimsy, and second because we do not construct the replacement with much scrutiny. For example, someone is being sad because they broke up with their lover, and while following the news sees how people in another country struggling with some sort of disease or disaster, and suddenly feels lucky to be alive and not in that country at this time, and thinks that it's not worth being sad, because life is too short. Two hours later that person would be sad again thinking of their misfortune with regards to their lover.
I won't argue that there is no use to emotions; clearly they are probably the sole reason the world is spinning.