It can be very hard, especially early on, not to worry about recurrence. And you are quite right, active treatment keeps you busy with other concerns, and reminds you that you are daily doing something constructive. Just taking tablets doesn't fill that gap. Then you start wondering what if...? It's very natural but it's also a result of looking back to fear and uncertainty rather than looking forward to being well and living your life. I found actively seeking positive things to do and think about a help. Do at least one thing a day you enjoy (may be quite small). Most of us have to go into training a bit to get back to assuming things in the world are going to be good rather than bad! Laughter is good medicine too. It will get better, but will get better faster if you practice. Best wishes.