Napoleon Bonaparte? Not the tune I had in mind, but that's not a bad idea. I think I'll try it that way.

Needed a few changes in the last half of the verse to scan. And I've stuck in an extra verse to match where the tune has been before. And, of course, you are more than wlecome to sing it any time:

Have you ever tried to sing a song,
And all at once the words are gone,      
And though you try to carry on
And finish anyway
Still everyone is watching you
"I wonder what he's going to do?"               
You wish the ground could swallow you.
And let you crawl away.
You feel quite naked and perplexed,
You've quite forgot your tuneful text,
You're standing there in dumb despair,
You don't know what comes next
Like you have stepped upon a stair,
And found too late there's nothing there,
Your feet and mind are re-aligned –
It's all just empty air.

It happened just like that one night,
The words just went out like a light,
I think they thought that I was tight,
And I could take no more.
So I bought myself a glass of beer,
And set it underneath my chair,
Then kicked it over, unaware,
It splattered on the floor.
And didn't I feel sore and vexed
My friendly drink was quite upset,
"Last Orders, Sir" – so no more beer.
Oh what would hit me next?
Like I had stepped upon a stair,
And found too late there's nothing there,
A vacant glass, alack alas,
All full of empty air.

But now I'll cut my story short,
I'll spare you all the full report,
But all at once I had a thought -
My cup did over flow,.
Bur didn't Jean Paul Sartre say
There's things against us everyday
No use to grumble anyway,
Philosophy can show,
When things fall out that can't be fixed.
No earthly use for getting vexed,
Just shake your head, and go to bed,
Prepare for what comes next.
And when you step upon a stair,
And find too late there's nothing there,
No good to rage, or shake your cage –
It's only empty air.

So if your words should fall apart,
Think on Napoleon Bonaparte,
And how at length he did depart
For Saint Helena's shores,
And did he rage and did he curse
Or did he mutter something worse?
Oh no, he sang a tuneful verse,
Rehearsing all his wars.
And in the South Atlantic he
Displayed such equanimity,
His hand he pressed across his chest -
And gazed out at the sea.
So when you step upon a stair,
And find too late there's nothing there,
Great Boney too fell, just like you -
It's only empty air.