Being happy or being not sad are not the same thing. Avoiding sadness is a signal of survivalism, someone trying to be safe and sound for another morning. Being happy is a symptom of living your life, a feeling that means "surviving isn't enough, we must feel alive". Animals can also show happiness, thus, animals also know how to live their lives (in their own terms) aside from just surviving, and that's (curiously) a sign of humanity. Are you feeling happy, or you're just not being sad?