Dear Friend

first i want to you to remember that when we have depression we suffer its symptoms. one is "Lethargy". we always feel tired and lack energy to do even the simplest task( for some even getting out of bed, brushing and taking shower is too tedious). also you always want to be left alone. when someone disturbs that, we get irritated as that the first reaction. the anger clouds any reason even if it is genuine. as in your case when your brother asked for your help you gave out the first reaction which is normal for any depressed person. then your mind starts to analyze and feels you have to help. but unfortunately people can't understand our first reaction and feel you won't help and show their anger towards us which is going to make worse things for us. so now you get caught into the guilt trap. so stop blaming yourself and convince yourself your mind is causing this. my suggestion would be when things cool down go to your brother and explain this and ask for forgiveness. there is no shame is apologizing for something which was beyond your control.