I had a bit of that experience - not depressed, getting on with life (worked through treatment) but a bit unsure of who I fundamentally was any more. Losing a breast was the least of my concerns, but I developed an arrhythmia - what I mentally named a Heart Condition (with capitals!). The me I knew didn’t have a Heart Condition! Was I some sort of quasi invalid? Should I be ‘taking things easy’, a highly unattractive thought? I discussed maybe needing a support group with my very smart senior oncology nurse. Who nudged me towards a one on one counselling session. Best thing I ever did. A good counsellor, who understands cancer but can also see beyond it, is possibly someone we all should engage, even for a short time as I did, cancer or no cancer! She sorted out my physical issues in no time and equipped me to deal with the underlying ones (a fear of ageing and death) myself. The insights she facilitated have kept working for me ever since. Best wishes.