Under these circumstances, interested parties would petition the court to appoint a guardian to act on your behalf. This is a necessary remedy, but there are drawbacks that can enter the picture.
First and foremost, the person that has the power to act on your behalf may not be someone that you would have chosen yourself when you were of sound mind. Secondly, there can be disagreements among family members with regard to the right person to act as your guardian. Disputes can slow down the process, and there can be lingering acrimony among family members.