My counsellor has told me that yes, a cancer diagnosis can cause PTSD, and in my case, most likely did. In most cases, it probably isn't the diagnosis alone that causes the trauma, but the culmulative effect of the treatments and invasive testing that is often necessary. Along with the high levels of stress that comes with the constant knowledge that you have a disease which could kill you. I had never heard of this before I started exploring it in therapy, but it is called Medical Trauma and there is some information on the web about it, particularly about cancer survivors and their increased risk of PTSD. I was told that I could have been vulnerable to PTSD because I, like yourself, was naturally an anxious person to begin with. The helplessness that comes along with such a diagnosis is traumatic, and unfortunately, it is something that is drawn out for years after the initial shock due to follow up testing. I would really suggest seeking help as soon as possible because the longer you try to shove the feelings down, the worse it might be in the end. Also, be patient with yourself. As far as cancer diagnoses go, yours is still very recent and it's not unusual to be feeling the way you are feeling. You may not even have processed all the feelings involved yet. I understand the feeling of waiting for the next blow. It may never happen, and in the meantime you are making yourself sick with worry. I am in the same boat. But please, don't do what I did and try to ignore it for years and years. If it is real trauma, it will not "just go away with time. Help yourself by asking for help.