My mom was diagnosed with breast cancer two years ago, and I've been exactly where you are. Assuming that there's nothing else major going on, I would guess that your sensitivity to the other issues is only a heightened response to your anxiety concerning your mother's condition. My suggestions would be :
1. Get your information about breast cancer in general, and her condition in particular. Gaining knowledge about the situation will more than likely give you a sense of empowerment. As Mal said, breast cancer treatment is one of the most well funded, well researched, and most treatable forms of cancer. People are fighting this every day, and your mom can too. Remember that your family is not alone.
2. Remember that there is no point in second guessing what she could have / might have done to improve her health or avoid this condition, other than to make lifestyle changes after she is through her treatment and on the way to remission. Deal with what's in front of you. I know it's hard, but when you've had the chance to to accept it you'll find you have more strength than you might have realized, and your mom is going to need to draw on you and your family.
3. In the same vein, give yourself time to accept it. It can be a rude awakening. Your response sounds fairly normal to this sort of thing, especially depending on your relationship with your mom.
4. Try to keep yourself busy. Exercise, read - but dwelling on it makes it no better, and you're the only one who pays the price. And I would back up the idea for seeing / consulting a therapist or someone else you can trust to talk to about it. The nice thing about therapists is that they have seen the symptoms of the emotional states you're going through, and often have standard coping techniques. This is all hearsay - being raised as a Southern male, we don't do therapists and counselors or life coaches or whatever they're called.
http://www.breastcancer.org/