confused by the ending ***spoilers***

I really liked this movie but I was confused by the ending. A couple of things happen abruptly and without much reason or explanation.

1. at her 'grand concert' she starts singing beautifully for a few seconds then she faints. I thought maybe this is just in the mind of her husband, seeing her the way she sees herself for the first time. I think some other people gasped and seemed to hear it also. Did this really happen or was it in their minds?

2. at her 'grand concert' when she collapses and coughs up blood. The doctor inspects her throat and says there is absolutely nothing wrong with her. So why did she cough up blood? I recall a dr saying it was a great deal of blood, like she was close to dying.

3. why did she suddenly become delusional?

4. why is it she can hear how off tune she is on the recording, but not when she's singing? If she's truly tone deaf, she would not be able to tell at all, like someone who's color blind. Which brings me to...

5. do you think she was really tone deaf or was it all part of the mental illness she had?

Maybe I missed something bc of the subtitles, then again I know that this is a French art film so random things happen for no reason.