In most, if not all states, medical bills, especially for emergency care, are treated differently than consumer debt in that if you make a regular attempt at payment, no matter how small, you cannot be sued. We have family friends in the exact same position as you that have been paying $5 to $10 a month for nearly two decades. This was not the payment plan they agreed on but after becoming disabled and not being able to work it is all they can afford.
Call or go online to your State Bar Association. Most have a lawyer referral service which allow you an initial consultation for a very nominal fee; in my state it's $20. Request an attorney familiar with consumer affairs. He/she can apprise you of the laws of your state. While there is some great information on this site, there is also a lot of uniformed/ bad information. This is too important for you to guess which it is you are getting.