Gänsehaut literally translates to "goose skin" but means "goosebumps" in English. It's a vivid and relatable word that captures a strong physical reaction to an intense emotion.
In the song, the singer uses it to describe the overwhelming feeling he gets when he sees the person he's falling for: "Ich hatte Gänsehaut" (I had goosebumps). This word perfectly conveys the immediate and powerful impact of love at first sight, making it memorable and engaging.
"Eine Nacht" is about the rush of falling for someone almost instantly. The singer sees the person and feels his heart stop, gets goosebumps, and can't stop thinking about them.
He imagines spending just one night and one day together and feeling like he could embrace the whole world. Being alone suddenly feels unbearable, and being with this person feels like coming home.
By the chorus he's convinced they belong together, like two voices in the same melody. What once felt confusing now makes complete sense, and for the first time everything in his life feels balanced.