Helpless & Guilty

I find myself feeling increasingly helpless and guilty as my son gets more and more sick. I feel helpless because I don't know what to do to make him feel better, if there even is anything I could do. I can't help but wonder if this is all my fault, if there's something I did or I'm doing that's making him sick. It's just so frustrating when I'm doing all the things the doctor is telling me to do and he's still in pain and vomiting and screaming all the time. Then I feel so guilty that I'm spending so much time with my son and seemingly so little with my daughter. I know that it's only because he's sick and needs more attention, but the hurt on her face when I can't come play right that second or help her fix something, or even get her more juice right then because she's thirsty, really tears my heart out. She just doesn't understand. She's trying to be understanding and help with the little things that she can do, but she obviously misses her mommy, and it kills me that I can't give her the attention she wants right now. I feel even more guilty and like a horrible mother for wanting sometime for myself away from it all. I keep thinking 'what kind of mom wants to be away from her kids? Especially a sick baby?' I know experts say we, as moms, need personal time to keep ourselves healthy, but for some reason it just feels wrong to want that. I'm really struggling to find a balance between Mommy/Wife/Me. I'm terrified to see what things are going to be like when I have to go back to work in a week. I'm sure that's going to bring on a whole new level of guilt.