A feeling of being sad or discontent is unhappiness. Your unhappiness about having to get up early on Monday morning might fade a little when you realize there are pancakes for breakfast.
The noun unhappiness is all about a state of being unhappy or, in other words, a lack of happiness. This can mean a feeling of deep sorrow, like your unhappiness when your beloved pet turtle dies. It can also mean dissatisfaction or displeasure: "Our teacher did not appreciate our practical joke. His unhappiness was clear when he made us all stay after school to clean up the shaving cream."