"She may have had asthma and emphysema because of her smoking," said Dr. Eric Braverman, an addiction specialist and author of the book "The Edge Effect." "From that, you can have a terrible respiratory arrest. You can have a seizure. Your lungs can choke off your trachea. It happens in asthmatics a lot."
Respiratory conditions might not have been picked up by Winehouse's physician.
"If you have a pulmonary disease, you need a lung function test, not a stethoscope," Braverman said. "So a simple physical that tells you you have a clean bill of health doesn't say much."
Winehouse's father told reporters in 2008 that she had been diagnosed with early-stage emphysema. She was also vocal about her struggles with eating disorders, which could have played a part in her death, too.
"You can also suffer cardiac arrhythmia from dieting and not eating properly," Braverman said. "Even panic attacks in her state can constrict the lungs and bring on death."
Kelly Osbourne and Mark Ronson were among the famous friends who attended Winehouse's funeral July 26, during which her family and friends sang her favorite song, Carole King's "So Far Away."
Winehouse's rep Goodman told Britain's Daily Mail that her father gave a touching eulogy at the ceremony.
"Mitch's last words to Amy in his eulogy were 'Goodnight my angel,'" Goodman said. "Sleep tight. Mummy and Daddy love you ever so much."
Reg Traviss, Winehouse's most recent boyfriend, attended the funeral and spoke to the Sun about the singer's death, saying "I have lost my darling who I loved very much." Blake Fielder-Civil, Winehouse's ex-husband, was not in attendance. He's currently serving a 32 month jail sentence.
ABCNews.com's Carrie Gan and Lara Salahi contributed to this report.