Hi Susie,
Firstly sorry that you are going through this.
While my situation is different to yours, I'm also newly diagnosed (with Stage 1 Non Hodgkins Lymphoma), and the diagnosis came right out of left field as I was also fit and healthy. Last week I felt as though I couldn't believe I have cancer as I felt so well.
I've just started chemotherapy, and as funny as it sounds, although chemo is not pleasant, I feel so much better now that something is being done.
The scariest part for me were the weeks between getting the diagnosis and waiting for tests, test results etc and then the dread and anxiety about starting treatment.
One thing that has helped me is to try and stay as positive as possible. I also do things like listen to relaxation and meditation apps when I'm feeling overwhelmed or can't sleep (there's loads of free ones that are good).
The Cancer Council Helpline staff are fantastic to talk too as well, and they can allay a lot of your fears.
Now that treatment has started I feel so much better within myself, and far less scared, so I hope you will find this too.
Take care,
Sue