An emotion is an arbitrary, personal and wholly subjective physical reaction. To what, you ask? An emotion is a physical reaction to the value placed on something.
In short, an emotion is an appraisal.
As an analogy, imagine the following.
You are about to sell your car.
What is the asking price and how do you decide?
Objectively you might look up the Kelly Blue Book value that most closely matches the year and condition and mileage.
But, let's make this more interesting.
Imagine that the car you are selling belonged to your only child. Your son. He took odd jobs after school and saved for it for several years until he could afford it. You went with him the day he finally paid for it with his own cash and you drove off the lot together singing a favorite song to the radio station that was playing. But, your son recently died of cancer after a lingering, unstoppable decline. Before he died, the dying son told you he wanted you to have his car and thanked you for encouraging him to earn it himself.
In your mind this car you are about to sell has more than a Blue Book value, doesn't it? A powerful subjective appraisal emotionally charged with memories and attachments goes along with it.
We can think of this as "value added."
But, change the scenario completely for a moment.
What if this car was not your son's car, but your own and it had a faulty emergency brake. A week earlier, the brake had failed and had rolled backward down the driveway badly injuring your pet Collie, Wilbur. After a few days of unrelenting agony, the Vet had to give a lethal injection to Wilbur putting him out of his misery.
In your mind, the car you are about to sell now has a different sort of appraisal, doesn't it? The connotations are negative now. The emotion you will feel parting with it are completely contrary to the previous situation.
In either case, the car is just a car.
But, your MIND, your consciousness places contrary evaluations depending on circumstance.
What is your mind? What is consciousness? How much context driven valuation drives your appraisal of mere "things".
What about people, animals, politics, religion? Are mere "facts" the only consideration in your view? Why wouldn't there be a host of mitigating or damning attachments?
Isn't the tangle of complications in your world view over-simplifed when you describe people, places and events out loud?
What about the layer upon layer of opinions, persuasions, influences and disciplines from babyhood by family, peers and heroes?
Have you chosen them? Or, merely absorbed them passively?
How unfettered by hidden appraisals can we be when we "love" "God" or pray?
What we think we've chosen, selected, appraised and valued---may be a collection of absorbed appraisals, valuations and second-hand, hand-me-downs.
The are Leftovers from a bygone era soaked into the fabric of our social consciousness. A stain we bear unthinkingly claimed as our very own point of view!
PSYCHOLOGY TODAY: http://www.psychologytoday.com/blog/hot-thought/201104/what-is-consciousness
But there is scant evidence for the view that minds are anything more than brains, so non-materialism does not seem to generate a barrier for explaining consciousness. Another possibility is that consciousness is just too complicated to be understood by human minds that evolved to find food, water, shelter, and mates in simple environments. But these minds have been able to create marvelous cultural tools such as written language, mathematics, and scientific instruments from telescopes to brain scanning machines. So it would be premature by centuries to give up on the attempt to find scientific explanations of mental processes including consciousness.