wonder how one stops worrying

People keep saying I look well - I suppose I look better than when I was on chemo but how do I know I am ok? When I got diagnosed, I felt better in all senses - physically and mentally - than I had for years yet I had breast cancer.
Now I don't feel as perfect as I felt then, thanks to side-effects from the medication I am on. The herceptin and tamoxifen combine to make me a little tired, well, pretty tired, especially stamina-wise, the herceptin makes me feel spacey at times and the tamoxifen gives me horrible hot flushes.
Would hate to have the cancer return. That's why I am taking herceptin and tamoxifen but they are not 100% foolproof.
My friend Tania's mom died of cancer on Friday but guess her circumstances were very different.
Would love to know how others feel on herceptin. I was told there were no side-effects until I started having them, The Lymph Lady told me about how most of her patients feel on it, and the oncology centre finally acknowledged that what I was feeling was legit and expected (except for the mouth ulcers which they claim is not from herceptin).