General opposites:
* Sad - This is the most basic and common opposite.
* Unhappy - A straightforward antonym, but perhaps less specific.
* Miserable - Implies a more intense state of unhappiness.
* Depressed - Indicates a more serious and prolonged state of sadness.
Opposites emphasizing specific aspects:
* Angry - If "happy" implies contentment, anger is its opposite.
* Worried - If "happy" suggests peace of mind, worry is the opposite.
* Frustrated - If "happy" implies fulfillment, frustration is its opposite.
* Anxious - If "happy" implies calmness, anxiety is its opposite.
It's best to choose the opposite that best fits the situation you're describing.