I can't add to what has already been said, except to agree with it all.
We all process this diagnosis differently, just like we all react to treatment differently. But I firmly believe that the grief hits us all in some way, at some point. For me, most reactions didn't come until all treatment was over. I started chemo 4&1/2 weeks after my diagnostic mammogram.
From the day of that mammogram I put one foot in front of the other to get through
Do what works for you, let the tears flow. You've heard that 3 word phrase "you have cancer", or a variation of it. It's life changing.
Take care