Miley Cyrus told Ryan Seacrest the allergic reaction that landed her in the hospital and forced her to cancel numerous shows was "scary" Monday in an appearance on his morning show, "On Air with Ryan Seacrest."

"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," said Cyrus, 21.

The weeklong hospitalization was due to an allergic reaction to Cephalexin, a medication presecribed to her for the flu, which she had been taking for five days.

On the sixth day, Cyrus woke up and knew something was wrong.

"I couldn't breathe and my skin -- everything -- was going insane," she told Seacrest.

While in the hospital, "I was begging the doctors let me out to go the show, and there was basically no way," Cyrus said.

But "I'm doing good, much better," the songstress told Seacrest Monday.

Cyrus announced rescheduled dates (and two new shows) on her Bangerz tour yesterday to make up for the shows she missed because of her illness.

The rescheduled Nassau Coliseum show is August 1.