Miley Cyrus opens up about "really scary" hospitalization

Miley Cyrus says she's feeling "much better" after an allergic reaction to medication landed her in the hospital and forced her to reschedule dates on her U.S. tour.

The "Adore You" singer, 21, called in to Ryan Seacret's radio show on Monday to talk about what happened and give an update on her health.

"So basically I had gotten sick while I was on the road," she explained on "On Air with Ryan Seacrest." After taking some doctor-prescribed medication for a "flu, cold situation" for five days, "on the sixth day I just woke up and it was ... so scary. I had basically been poisoning myself for a week with something I didn't know I was really scary allergic to."

"I never thought I was gonna get stuck in there for as long as I did," she added. "I thought it was maybe gonna be a night, and I was actually there for five or six days."

Cyrus said she's allergic to penicillin and while that isn't what she was prescribed, it was a different medication in the same drug class that caused the reaction. She also told Seacrest that while she was in the hospital, she was most upset about "not being on the road."

"I would feel good ... [and ask doctors] 'Can I go? Can I get back on the stage?' That was the hardest part. ... I was just crying because I was so bored," she added.

Now out of the hospital and gearing up for the European leg of her tour, Cyrus said she's on the mend.

"I should be all good, but what was the worst is that this reaction can happen from five to 27 days," she explained. "But I've been really good, and now, I just have to be more careful."