That's rough and life never seems to just give you a time out to make sure you can give your complete focus to what is most important to you at the moment.
For your own sake try not to project or displace your anger and frustration onto others as that will of course make them feel bad and in hindsight you'll feel bad about that and also it won't help anything. If you need a chance to yell and vent and get everything out then take a short break from work and do that just so you're not dragging others down, you're not digging a hole for yourself, and you're not wasting emotions on events other than what you are actually worried about or wanting to focus on.
I do hope things turn around for your mother soon. I hope you are able to feel better and yes there is a sense of powerlessness, but you can only control so much of your own life...other people's health isn't something you can affect unless you're a doctor. You CAN affect other people's attitudes and a good positive attitude is one of the best weapons you can have in a medical situation, it's not the end all be all, but it's better, easier, and treatment is more effective with a happy patient than a depressed one, so stay focused, stay strong for your mother, and maybe let your co-workers know what is going on if they will be supportive of you (and I know not all work forces are supportive).
"Drown in a vat of whiskey.....death where is thy sting?" - W.C. Fields.