I know someone that immigrated to EU from middle east, after ~1 year developed a severe life threatening stomach/liver illness(can not recall the details), went through multiple operations, after 1.5-2 years away from work but getting most of his salary due to welfare got better and got back to work. He is very young and I suspect you could have anything close to this in US. Let alone immigrants, even citizens can not afford to do this.
I have never lived in the US and this all from online media, reading and talking to various ex/current US citizens/residents colleagues, so I might be wrong still.
As someone who has lived in various parts of the US and knows people across the economic spectrum I only know of one person who has had major issues with medical coverage in the US. Various complaining about doctors and treatments and so on but that's the case in all countries.
edit: And my comment was more to point out that anecdotes make poor facts.
I have never lived in the US and this all from online media, reading and talking to various ex/current US citizens/residents colleagues, so I might be wrong still.