United Kingdom, July 5 -- Jessie J regrets not saying "goodbye to her old breast" amid her mastectomy.

The 37-year-old singer underwent the surgery after being diagnosed with breast cancer and admitted she went into survival mode and is now experiencing some "delayed sadness and frustration" as she starts to process her ordeal.

She wrote on Instagram Stories: "My experience was when I got diagnosed I went into survival mode.

"There was so much going on with appointments .

"I didn't really have a lot of time to process what was happening or what was going to happen. So I'm currently experiencing some delayed sadness and frustration by having time to process what IS happening. A little disappointed in myself I didn't say goodbye to my o...