Sobrepensaba comes from the verb sobrepensar, which means to overthink. It's a modern and increasingly common word in Spanish, reflecting a contemporary struggle with anxiety and rumination.
In the song, the artist longs for his past self,
Eden Muñoz's "Mi Yo De Antes" is a really relatable song about looking back at a past self with a bit of nostalgia and longing. He sings about feeling stuck, like "Hay algo en mí que no me deja ser" [There's something in me that won't let me be] and how a bad streak is making it hard to see the good. It's all about the struggle of growing up and realizing that life doesn't come with a manual, as he says, "Nadie nos dijo que crecer dolía y vivir no viene con manual" [Nobody told us that growing up hurt and living doesn't come with a manual].
He misses his old self, the one who didn't overthink everything and just bounced back from hurt, "Me gustaba más mi yo de antes, la versión que no sobrepensaba" [I liked my old self more, the version that didn't overthink]. He even talks about walking in the rain to hide his tears, making people think he's fine: "Pa' que el agua le moje los ojos y hacer que la gente se confunda / ¿Qué sé yo? Que no va llorando, que está mejor que nunca" [So the water wets his eyes and makes people confused / What do I know? That he's not crying, that he's better than ever]. It's a really honest look at the fears and anxieties that come with adulthood, compared to the carefree days of youth.