Hi IG,
I too relate to your post. I lost my patience/temper with my Mum many times even though much of what I was frustrated about related to her mental illness and meds. I shouted down the phone and really upset her on several occasions. There was one thing I said when I was 17 that I still feel incredibly guilty about 12 years later.
Before she died last year she asked me to get her an emergency alarm to wear round her neck and gave me the number of her social worker to ring and arrange it. I didn't get round to it. She was found dead in the hallway of her flat and she'd been there for hours. It haunts me that she could have spent her dying moments thinking 'if only she had got me that alarm'.
All I can say is that I empathise so much with what you're feeling. I hope you can make peace with these feelings; you are clearly such a good person because you truly care.