Sole caregiver, what happens when I have issues of my own or when I'm gone?

My mother is in a nursing home and so is my MRDD sister. Mother has mild dementia, I bring her home every day for 2 hours, and to visit my sister Sundays. Mom is at a facility across from work, sister 10 min away both 15 min from home. Perfect situation but still a lot of work, long story as to why. I'm Guardian of my sister there's a lot of paperwork and both need an advocate of course. Last week I felt like I was having a heart attack and went to ER. My heart was fine but I was so stressed about being alone and having no one and that I had to take care of them that I discharged myself. I ended up being fine but my question is what do you do when you have no one to take care of you and your the sole caregiver? I have been in and out of the hospital with my mom and my sister and the last thing I need is for me to be there. This time I was lucky but who knows what's going to happen to me next.