Miley Cyrus was finally released from the hospital following a "severe allergic reaction" to some medication she had been taking for a cough. The 21-year-old pop star was hospitalized early last week and opened up about her mystery illness for the first time with Ryan Seacrest on his radio show.

"I'm doing good," Cyrus told Seacrest. "I'm much better - happy to be on the phone with you guys, happy to be getting back on the road. You have no idea."

Cyrus admitted to the "American Idol" judge that she didn't expect to remain hospitalized for so long and couldn't help but cry almost every day she was in there. The singer's hospital stay lasted about five or six days.

"It was so scary," she said. "When you're allergic to something you're basically poisoning yourself. I had basically been poisoning myself with something I didn't know I was really scary allergic to."

Cyrus explained to Seacrest that she had come down with a cough while on tour and was prescribed antibiotics to treat it. She said she had been taking the medicine for five days and on the sixth day, she woke up feeling really sick.

The pop star was immediately rushed to the hospital where doctors told her she was having an allergic reaction.

"Every two or three hours, I would be ok and then all of the sudden it would happen to me again," she continued, referring to her allergic reactions. "It was insane. I was begging the doctors, 'Let me out to go to the show!' it was basically no way."

Because of her hospitalization, Cyrus was forced to cancel shows in Nashville, Louisville, Kansas City, and St. Louis.

The "We Can't Stop" singer is expected to resume her tour on May 2 when she starts the European leg in Amsterdam, Netherlands. The dates she had to cancel in the United States will be rescheduled this summer beginning Aug. 1 in Uniondale, New York and ending Aug. 14 in Chicago, E! News reports.