What makes your heart sink

Today I read one book, which is quite interesting.
It is about how to give a sensational speech, so I keep reading.
The author suggested that we should talk about what makes our heart sink.
At first, I am quite confused, I can’t find the obvious link.

Then I understand, if it really means to you,
and if it is something that you really want to,
then you can express it well with emotion.
That’s the secret without any question.

But I struggle to find the answer.
What makes my heart sink, with myself, I whisper.
Is it when Manchester United lost?
Or is it when I see medical bill and know how much it costs?

Is it when I have an argument with my wife?
You know the answer, I will always lose that fight.
I still can’t find the answer, you see.
But I take this as a good news to me.