Bellizcame is a colloquial way of saying "pinch me." It comes from the verb pellizcar, meaning "to pinch."
In the song, the singer is in shock and disbelief about a breakup, asking "Bellizcame, dime Jesús una pesadilla" (Pinch me, tell me Jesus it's a nightmare). This word perfectly captures the feeling of being unable to believe a difficult reality, making it both relatable and memorable.
Ever been completely blindsided by a breakup? That's the heart of "¿De Qué Me Perdí?". The singer is in total shock, asking, "What did I miss?" One moment, they were in a shared "historia" (story), and the next, their partner has decided, all on their own, that the relationship is over. The singer is left reeling, demanding an explanation for how things went so wrong so quickly. They plead for a simple breakdown of the situation, because the news is just too shocking to comprehend.
The pain and disbelief are so intense that the singer hopes it's all just a "pesadilla" (nightmare) and begs to be pinched awake. There's a deep fear that this sudden change is because of someone new, hoping their partner isn't feeling "cosquillas" (butterflies) for another person. The news has made the singer's smile "disappear," capturing the raw feeling of having your world turned upside down without any warning.