I really can relate to your feelings. At about my 3rd year post treatment somehow I became more aware of the "dark shadows" that can be a part of survivor doubt. At a conference conducted by an oncologist (who was a breast cancer survivor) she emphasized the normalcy of such doubts and fears. Her point was that we as intact women are diagnosed with a potentially life-threatening illness. The fact of the diagnosis.. in a moment.. changes our lives. We then feel vulnerable and that is very difficult to shake. Decisions regarding treatment are made quickly and echo through the months of determination to survive and be well again...be intact again. All of this stress of battle is without significant preparation and ongoing counseling. She strongly suggested adding to every treatment program a traumatic stress component to help with life adjustments after breast cancer. I really agree with that.
I am now 5 years out from treatment and rarely think about recurrence but you are so right every October it surfaces for a while but then it seems to settle back into the background...and any "dark shadows" never take over...WHEW! I now volunteer for Reach to Recovery for the America Cancer Society...that really helps.