I feel like I need to suppress my illnesses because my MIL has cancer

We recently got some bad news that my MIL has cancer that can’t be surgically removed so chemo is the only option. I’m so saddened by the news, as she’s a wonderful MIL, no drama and always willing to help out. I have two auto immune diseases, which I’ve had for 11 years and have recently come out of remission, making me feel very nauseous and weak (vomiting, diarrhoea and bleeding). I just came out of hospital today, my doctor says one of the diseases currently has a high chance of giving me colon cancer.

So I’ve been feeling really ill, but I also feel really guilty because my MIL has it so much worse. I’m having a hard time trying to hide that I’m feeling unwell. I really want to sleep and rest, but I’m also the primary carer for my two year old, so by the end of the day I’m feeling so sick and exhausted.

Of course my husband wants to go out and do activities with our family and his mum, and I 100% support it and want to go too, but I feel so sick. I feel really horrible when he asks why I can’t come with sometimes, he doesn’t say it in a mean way, but I think my illnesses are not severe enough to be concerning but at the same time are bad enough to stop me from doing certain things.

There’s days where I wish was cared for and didn’t have to think about what to make for dinner or what pjs my child needs to wear etc, but then feel so guilty because my husband works 9-5, 5 days while trying to process his mum.

I’m not sure how to feel or how to act. Does anyone have any advice? Thanks so much in advance