The Kath and Kim actress, who signed up as the face of Australian weight loss company Jenny Craig in 2009, said that she needed a machine to help her breathe at night and was always in pain before she lost 25kg.
Szubanski told New Idea magazine: "In my darkest moments, I was frightened that I would shorten my life considerably and be wheelchair-bound."
The 49-year-old also revealed that she is looking forward to her upcoming 50th birthday now because she has never felt more healthy. She said: "I feel amazing. It just keeps getting better."
Szubanski was recently photographed in a swimming costume and admitted that she loves working out at the beach. She said: "I've always swum and enjoyed the beach. I think it's vital that people of all shapes and sizes get out and be active."
A movie version of Kath and Kim was mentioned in reports last month, although Szubanski said that her "lips are sealed" on the matter.