Speaking at Madrid's opera house alongside one of the doctors who treated him, the 72-year-old Domingo said he had felt unwell after a rehearsal and quickly sought medical help. The tenor said Dr. Carlos Gonzalez then detected a case of deep vein thrombosis and applied the appropriate treatment.
"I thought I would return from the check-up straight away back to the rehearsal," Domingo said. "But I was told, 'No, there is something serious here'."
Gonzalez explained that a blood clot had formed in Domingo's right leg and moved up to his lungs where it then lodged in an artery. He said it was not an unusual condition, and that it was often linked to spending hours sitting down on long flights.
"It sounds catastrophic, but it didn't turn out like that," Gonzalez said. "We established an early diagnosis, and there should be a good recovery, a complete and full recovery."
Domingo said he had studied Giuseppe Verdi's "Giovanna d'Arco" during the five days he was in the hospital, and he hopes to be well enough to sing his part in it at the Salzburg Festival in early August.
"I tried to cancel it," the Spaniard said, but he was told by festival organizers that the baritone they had to replace him hadn't fully learned the role, so he decided to continue.
"He also looks forward to keeping his engagements in Verona where he will sing and conduct 'Operalia,'" said Nancy Seltzer, the singer's representative in the U.S.
Domingo spoke just before attending a piano dress rehearsal of Daniel Catan's "Il Postino" in Madrid on Sunday evening, a day after being released from hospital. The hospitalization forced him to cancel a handful of appearances, including six shows of "Il Postino" at the Spanish capital's Teatro Real.
"I am very sad not to be able to sing in today's dress rehearsal," Domingo said. "My doctor has told me that with a degree of caution, everything is still possible. I have been very well looked after."
Alvaro Domingo, the tenor's son, told The Associated Press earlier that he expects his father to spend three weeks recuperating in Madrid and that the singer isn't contemplating retirement.
On Sunday, Domingo addressed the media alongside Gonzalez as well as his two young grandsons, Placido and Alvaro.
The Spanish opera star has maintained a vigorous schedule since recovering from colon cancer surgery in 2010. He said he had already worked out "very lightly" on an exercise bike.
Before going in to see the dress rehearsal, Domingo sang the first few bars of "Il Postino" to journalists.
AP Music Writer Chris Talbott in Nashville, Tennessee, contributed to this report.