Vaivenes literally translates to "swings" or "oscillations," but it's commonly used to mean "ups and downs" or "fluctuations." It's a more evocative and less common word than simply saying "altibajos."
In the song, Leonel Garcia uses vaivenes to describe how life is full of constant movement and changes, much like the tide. It perfectly captures the central theme of the song: the unpredictable, ever-changing nature of life, which is "happy-sad."
Have you ever felt like life is a constant rollercoaster? That's the heart of Leonel Garcia's song "HAPPY-SAD." He describes life as an eternal, dizzying movement, swinging back and forth like a pendulum or the ocean's tide. One moment, life is a beautiful melody that guides you, and the next, it's a confusing noise. It can surprise you with an unexpected setback, like a "golpe por el lado ciego" (a blow from the blind side), but it can also present a brand new opportunity, like "una puerta que se abre de nuevo" (a door that opens again).
The song's main message is right in the title: life is a mix of happiness and sadness. Garcia sings that one day you laugh, the next you cry, and then you simply start all over again. He lists a series of powerful contrasts to paint a picture of the human experience: wealth and poverty, being free and being a prisoner, storms and calm skies. It's a beautiful reminder that life is full of ups and downs, and these opposing forces are what make every day unique and "irrepetible" (unrepeatable).