Experiencing fear of recurrence as someone affected is very common. In fact, it is one of the most common difficulties you can experience after treatment is over. Fear of recurrence is therefore a completely normal reaction—it is significantly more common to experience it than not!
It is the circumstances that have been abnormal. Most people do not have to go through cancer themselves. Being forced to go from a life without cancer to a life with cancer is to be thrown into something completely unknown, and before you have been there yourself, it can be difficult to understand. Just something like daring to be physically close to another person again. Daring to show yourself naked or daring to have sex can have become one of the most frightening things there is.
Cancer is cruel in this way: in addition to threatening to take the life of the person affected, it can cause body parts and bodily functions to be lost. Cancer can bring about all kinds of fears and affect the relationships we care about.