Despertémonos is the plural imperative form of the verb despertarse, meaning "to wake up." It's an interesting word because it's a command directed at a group, specifically "us."
In the song, the artist sings, "No te hagas la loca toda la noche entera, despertémonos mañana con ganas de repetirlo cuando quieras." This translates to "Don't play dumb all night long, let's wake up tomorrow wanting to repeat it whenever you want." It's a playful and suggestive invitation, making the word stand out in the context of a romantic encounter.
Noriel and Manuel Turizo build this one around a single accusation: you're still into me, so quit pretending otherwise. The hook says it straight, 'Ay no te hagas la loca' [Oh, don't act like you don't know], and the verses back it up with small, specific proof rather than vague feelings. He remembers 'A veces pienso en tu boquita cuando amanece' [Sometimes I think about your little mouth when dawn breaks], then turns the same claim back on her: her friends have noticed that 'Se han da'o cuenta que todavía no me superas' [They've noticed that you still haven't moved on from me], and whatever she tells them, 'Pero con ninguno funciona' [But it doesn't work with any].
Midway through, Noriel steps in for a solo verse and admits he tried the same trick himself: 'Trate de buscar en otra lo que una vez contigo tuve' [I tried to find in someone else what I once had with you]. It's built for a room to shout the hook back, and by the outro the lyrics drop the story completely and just call out names, Noriel, Manuel Turizo, and the rest of the crew, before the beat cuts out.