TAMPA — Paul O'Neill, creator of the Trans-Siberian Orchestra, died in a Tampa hotel room last month from a drug overdose, an autopsy released Tuesday states.

O'Neill, 61, had a history of heart disease, but ultimately died April 5 from a combination of methadone, codeine, diazepam and doxylamine, a medical examiner wrote.

He made no mention of his health when his daughter dropped him off at the Embassy Suites on the University of South Florida campus earlier in the day, the Hillsborough County Medical Examiner's Office reported.

Later that day, though, O'Neill's daughter found him dead on the floor after breaking into his room with hotel staffers and university police.

O'Neill had a prescription for the painkiller Tylenol No. 3, which contains the opiate codeine, likely to combat pain from age-related arthritis in both of his hands and osteoporosis in his back and left arm, said Julia Pearson, chief toxicologist with the Medical Examiner's Office.

He also had a prescription for Valium, a name-brand version of the anti-anxiety drug diazepam, and he had used an over-the-counter sleep aid, Unisom, that contains doxylamine, Pearson said.

While methadone is commonly prescribed to help treat heroin and opioid addiction, it is just as commonly used as a painkiller, Pearson said, adding that people dealing with chronic pain may take more than one painkiller at a time.

However, when taken together and in large doses, the drugs in O'Neill's system could easily turn deadly, she said. The sedatives would have caused O'Neill's heart rate and central nervous system to slow, then caused him to fall asleep and stop breathing.

"With these kind of drugs interacting together, he likely had a very painless death; just fell asleep and never woke up," Pearson said.

Shortly after he was found dead, band members announced that O'Neill died of a "chronic illness." According to his autopsy, he suffered from hypertensive cardiovascular disease and coronary atherosclerosis, as well as tinnitus, TMJ disorder and a neurological disorder called "prosopagnosia," which made it difficult for him to recognize the faces of familiar people.

His drug abuse, however, caused his death, the medical examiner determined.

O'Neill managed rock bands including Aerosmith before creating the Trans-Siberian Orchestra in 1996. The group was inspired by acts such as Pink Floyd and Emerson, Lake and Palmer, O'Neill said in 2008. It quickly became renowned for grandiose Christmas concerts that merged full orchestral arrangements with heavy-metal laser shows and pyrotechnics.

O'Neill split his time between his home state of New York and the $1.6 million home he and his wife purchased in 2010 inside the Reserve, a gated community in Tampa Palms.

Tampa was the base of his musical operation. He purchased a studio from Morrisound Recording in 2014. The band recorded there, minutes away from the hotel room where O'Neill died.

In 2016, Trans-Siberian Orchestra was the 16th-most-successful touring act in North America, playing 104 shows to nearly 960,000 fans and grossing $55.3 million — more than tours by Kanye West, the Dixie Chicks or Rihanna.

O'Neill rarely played with his orchestra outside of the final few minutes of their Tampa concerts, radio DJ and friend Mason Dixon told the Tampa Bay Times in April. An ankle injury kept him from performing during the orchestra's last Tampa appearance, which drew more than 30,000 fans to two December shows.

Still, O'Neill watched both performances from a seat by the soundboard, clad in his trademark sunglasses and black leather jacket. Keeping with tradition, he donated a dollar from every concert ticket sold to a local charity, Dixon said in his interview, estimating that over the past decade or so, O'Neill donated more than $200,000 to Mason Dixon's Christmas Wish Fund.

Contact Anastasia Dawson at adawson@tampabay.com or (813) 226-3377. Follow @adawsonwrites.