The 31-year-old was having a 'routine' procedure to remove scar tissue from her oesophagus, following the horrific acid attack she suffered in 2008.
But something went wrong, causing Katie severe pain and resulting in her losing a worrying amount of weight.
She told the Mirror: "I went in for a routine operation to remove scar tissue from my attack but there were complications.
"I was discharged but started to deteriorate. It's been very painful and I've lost a stone in 15 days so I had to come in and be monitored."
Katie added that she hopes to be reunited with her fiancé and one-year-old daughter Belle soon. She said: "A stone is a lot and I look like a skeleton but hope to be back home and back to normal asap – all fun and games."
Her illness meant Katie was forced to pull out of an event to promote her new book Beautiful Ever After.
She took to Twitter to apologise to fans, writing: "So sorry to have 2pull out of tonight, I am incredibly frustrated as I hate it when my injuries get in the way of everyday life. I'm very ill."