Guilt is kind of crippling isn't it? It sounds to me that you have a low self esteem, forgive me for saying so, do you feel that is the case?

I want to tell you that there's no reason for you to feel guilty for doing such a thing - sometimes it's necessary to excuse yourself on account of depression and there's nothing wrong with that. I think it's very noble of you to always put others first but I think it's also very important that you love yourself as well. Maybe in the future tell yourself that it's okay to take space, and also maybe consider being honest with people about the reason you are taking space instead of making up some other excuse. Easier said then done, I know, but honesty is the best way, it'll help you to have healthier relationships with people and also build up your own self worth.