Is this sentence correct? 'I fell down at the door'
'I fell down at the door'
Does it mean: 'I fell down on the ground in front of the door'

Which phrase is used in spoken/informal English?
Which phrase is more common?

Question

Is this sentence correct? 'I fell down at the door'
'I fell down at the door'
Does it mean: 'I fell down on the ground in front of the door'

Which phrase is used in spoken/informal English?
Which phrase is more common?

Answer

"fell down at the door" is perfectly correct.  It sounds a bit formal.   
"fell down by the door" is also correct, and is more colloquial.  
However, those two phrases don't automatically mean "In front of" the door.  The person could have fallen down to to side of the door, or, from the point of view of the speaker, behind the door.

Answer

I would say
I fell in front of the door
by saying you fell (have fallen) implies you 'hit' the ground.

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