I am new to the bcna site and was trying to find more information about DCIS when I read this post.
I am 49 and was diagnosed with DCIS in 2015 when I found a big lump on my left breast. I had a nipple sparing mastectomy as the tumor was big (4cm) and my breast very small. I was told there was no need of any other treatment apart from surgery and thought I'd have to worry only about the right breast.
Last Dec I found another lump close to my nipple during my regular annual checkup and had another surgery on the same breast I had previously had the mastectomy.
This time, the surgeon recommended either radiotherapy or hormone therapy. I'm thinking in doing radiotherapy and avoid hormone treatment as the side effects are not nice.
Just make sure, you continue doing regular checks as there might be recurrences even after mastectomy. The chances are very low 1-2%, but as you can see, it happens.
As you said, one's life can change in a blink of eyes, but it's important to keep calm and deal with things as it comes. I live in the present and try not to overthink about the future. You must have some headspace.