Pesadilla translates directly to "nightmare." It's a vivid and evocative word that immediately conjures strong imagery.
In "Así Sucedió," Juan Gabriel uses this word to describe the end of a relationship, singing, "Al fin despertamos tú y yo de esa pesadilla" (Finally, you and I woke up from that nightmare). This powerful metaphor conveys the pain and relief of moving on from a difficult experience, making it a memorable and impactful word in the song.
Juan Gabriel sings about a relationship that ended quietly, without drama. Two people came together out of curiosity more than deep love, shared some affection and a lot of conversation, and then simply stopped. There was no argument, no dramatic goodbye — just silence.
The title, "así sucedió" ("that's how it happened"), is the singer's own shrug at the end: this is simply what occurred, not something anyone fought against or tried to stop.
The closing lines compare the whole relationship to a strange dream, so wonderful it barely felt real, and waking from it feels like waking from a nightmare. It's a classic bolero mood: tender, a little wistful, accepting rather than bitter.