Lunatica literally translates to "lunatic" or "moody," deriving from "luna" (moon), reflecting the old belief that the moon influenced mental states.
In this song, Vasco Rossi uses it to describe life itself as "così lunatica" (so moody/fickle), highlighting its unpredictable and ever-changing nature. It's an evocative word that captures the song's theme of life's unpredictable ups and downs, making it both memorable and central to the song's message.