Not paying a bill affects your credit rating and will make institutions less likely to loan you money.
If the amount of money was very large,
there could be more serious issues.
If you are an American citizen,
you can enter this country whenever you want...but call an attorney in the US or Legal Aid (reduced or free legal advice).
If it were me,
I would go to Legal Aid,
open a case and see what your "status" is - what the hospital you did not pay did with the case.
Why wonder and "look over your shoulder"?
Look up Legal Aid,
find out and take charge of your life.