from a 2008 NPR article on Lucia di Lammermoor, a few words on the opera in general and then the aria's scene specifically:
"Of all of opera's unhinged ladies, the title character in Gaetano Donizetti's Lucia di Lammermoor sets something of a gold standard for going bonkers. Forced into marrying someone she detests, Lucia stumbles into act three, wielding a bloody knife, freshly used to slice up her betrothed, all the while hallucinating and rambling on about the man she really loves."
Back at the Castle, the wedding party is still in full swing. But everyone freezes when they see the look on Raymond's face. He reports that while checking up on the newlyweds in their chamber, he found Lucie, bloody dagger in hand, standing over the body of her new husband, clearly out of her mind.
Lucie herself appears, in a bloodstained nightgown. It's her big mad scene — a 15-minute rollercoaster ride of incredibly florid music — a challenge for even the best sopranos to get right both technically and dramatically. In her delirium, Lucie hallucinates. She imagines herself back with Edgard, about to be married, but she also flashes back to her dream from Act One — a dead woman at the fountain trying to separate them. The wedding guests look on in horror, and Lucie finally faints. Henri returns to find his sister crazed and Arthur murdered.