Doctors have to eat,also. Discuss financial problems with them and if they won't give you a discount, pay as much as possible each month. As long as you pay something, they cannot take you to collections, even though they threaten. I know it is difficult; my immigrant(legal) spouse is unable to get medical coverage, and he now has peripheral artery disorder. We had to go to a clinic which gives him a discount.
Again, it isn't easy, but I was in the medical field, and many, many people came to me for treatment, and then did not pay me. I lost thousands, even though everyone else charged $100 a visit and I charged only $25. It still hurts that they took advantage of my being caring toward them. So, please don't think doctors and others in the field are making a lot of money. Some are, and they hopefully will get punished somewhere in another life. But, the overhead, etc. that I had to pay was not seen by my patients; they thought I was rich. I finally had to retire, because I was treating people (a lot of drug users and alcoholics) and they skipped out on me.
Don't wait for collections. Make a call or appointment and make arrangements; they would rather get something other than a filing of bankruptcy when they get NOTHING.