Anna Gunn stunned at the Emmy Awards on Sunday night -- where she revealed the shocking reason behind why she looks so different on "Breaking Bad."

"I was actually ill while I was filming the show and it affected my weight," Gunn told PEOPLE about her changing on-screen appearance, which has (unfortunately) prompted negative reactions from fans in the past.

"They gave me cortisone and I puffed up and gained weight," she added. "Now I'm better, thank God."

Better than ever, actually.

Gunn picked up a much-deserved trophy for Outstanding Supporting Actress for her role as Skyler White at the event -- and looked gorgeous in a Romona Keveza gown.

As for how she stays in shape now, Gunn says "I run around after two kids" ... and does Pilates.

See more stars who have struggled with weight criticism in the gallery above!