I think it's perfectly normal to automatically seek out life-affirming experiences in the face of death. For you, that meant wanting to train.
Wanting to live life is never bad. Resenting death and illness for sucking away life is never inappropriate -- we need to accept it, but we don't have to be happy about it. There's no need to feel guilty over wanting to go to the dojo, and feeling upset that your mother's illness deprived you of an opportunity to train. You resent the illness, not your mother -- there's nothing to feel guilty about.
I lost my mother, my father, and my best friend within five years of each other. There are still nights when I wake up and feel completely lost -- when you lose the people close to you, the pillars in your life personified, you feel adrift. Sometimes it doesn't feel survivable, but it is. You grow new pillars, maybe not as strong as the ones that were there for you from birth...but strong enough to hold you up.