I have unfortunately experienced this two times already. You cannot even go and open the door for the emergency. Sure, you can let them break down the door, but that is not ideal (and to fix it will be expensive). Does at least your neighbor have keys to your apartment for such case?
And after they patch you together in an emergency room and send you home, and you can barely walk, who will help you get to the toilet?
Who will take care of you?
If you have no one (a roommate, a brother, a friend, a spouse), you should work on having such relationship(s) as soon as possible. It is not a question of if, but when, you will need someone to help you.
Money can get you so far, but having someone who cares about you is priceless.
It also goes the other way. Would you be able to drop everything and go take care of someone for at least a week or two until they get better? What about a couple of months or years?
Fortunately, I had my wife and family, who helped me take care of me and my son. And I try to not take it for granted. I am grateful that I have such amazing people who care about me in my life. And will try to keep them there and add new ones whenever possible.