It’s natural for you to feel scared. You obviously love and care for you mother and feel a lot of empathy for what she is going through. I agree with @dabbler that I’m not so sure that hiding your fear and worry is helpful to her. Yes, you have to make her feel positive and strong by being strong yourself. She is going to need to lean on you in a way that she may never have had to before. Now you’re old enough to be there for her when she needs you as she was for you growing up. It may be a difficult shift for both of you.
I have some mixed feelings about the whole issue of showing emotions in this kind of situation based on my own experience. You see, in my family, we have never been good at being open with our emotions. There is much love and caring, and not really an inability to express emotion, simply more of an awkwardness about it, a discomfort. I’m not sure why, it’s just always been that way.
When I was 19 I had cancer and one of the weirdest things about it was how we (my entire family) didn’t really talk about it. We had to go to the doctors together, my mother nursed me and cared for me, but the idea of dying, the idea of fear, that was just never talked about. I was complicit in it because I think if I had talked about it, they would have been more emotive and open also. As it was, it was an awkward situation. The only time that made me angry was when my mother, in a protective,well meaning effort to keep me from being overly optimistic (lest I be disappointed later) downplayed the results of my first chemotherapy session. I had had a large swelling on my neck and after my very first treatment I noticed it had been reduced in size quite a bit. I went to her very excited to show her how the treatment was working. She told me not to get too excited. I know that sounds mean, but she didn’t mean it to be. She didn’t want me to have false hope. I guess she wanted me to know that it might be a long road to recovery and there was no magic bullet. Thing is, I knew that. I felt very hurt and angry at her response.
But what does this have to do with you? I think it says that honesty and openness and talking about things, not hiding them, is better. No one really knows how good a prognosis someone has. I was told by my doctor that in such cases (that is, in my stage of the disease) “we don’t hope for a cure, we just hope to keep it under control”. That made me angry too. I was afraid, but I was a fighter. I can consider myself cured at this point. It’s been a long time.
How can you help your mother? Ask her. Mom, what can I do that will make this easier for you? I want to help in any way that I can. Please feel that you can be open with me. Let me know if you need anything
Simply saying that you are there for her, and showing her that you are strong enough to deal with her fears and her weaknesses, will mean an awful lot to her.
I agree that crying and hysterical jags would increase your mother’s trauma and are not a good idea. But a fake cheeriness that makes it hard for her to break through to you and be honest with you is not the answer either. Just be yourself and be as open as you can be with her. Don’t pretend not to see when she’s having a physically hard time of it. Try to keep life as normal as possible. Don’t treat her like a patient or victim. She’s the same person she always was.
You sound like you have a good head on your shoulders. I wish you all the grace and strength you will need to get through this. We are all capable of so much more than we know. It is in being tested by life that we find this out. If you ever need some emotional support feel free to PM me.