お願いします。オードリー・ヘプバーン主演の映画「マイ・フェア・レディ」の挿入歌に、『I Could Have Danced All Night』があります。

Bed, bed I couldn't go to bed
My head's too light to try to set it down
Sleep, sleep I couldn't sleep tonight
Not for all the jewels in the crown

I could have danced all night, I could have danced all night
And still have begged for more
I could have spread my wings and done a thousand things
I've never done before

I'll never know what made it so exciting
Why all at once my heart took flight
I only know when he began to dance with me
I could have danced, danced, danced all night

It's after three now
Don't you agree now?
She ought to be in bed

I could have danced all night, I could have danced all night
And still have begged for more
I could have spread my wings and done a thousand things
I've never done before

I'll never know what made it so exciting
Why all at once my heart took flight
I only know when he began to dance with me
I could have danced, danced, danced all night

I understand dear
It's all been grand dear
But now it's time to sleep

I could have danced all night, I could have danced all night
And still have begged for more
I could have spread my wings and done a thousand things
I've never done before

I'll never know what made it so exciting
Why all at once my heart took flight
I only know when he began to dance with me
I could have danced, danced, danced all night

文中の
I only know when he began to dance with me
I could have danced, danced, danced all night　
はどのように解釈すればいいのでしょうか？
I only know when he began to dance with me.で一文、I could have danced, danced, danced all night.で一文なのでしょうか？
それとも I only know の know の対象は when he began to dance with me. I could have danced, danced, danced all night. なのでしょうか？
もしそうであれば,I could have danced, danced, danced all nightの解釈はどうなるのでしょうか？