Green’s Dictionary of Slang

1. very drunk.

1812		Vaux Vocab. of the Flash Lang.
1834		‘The Corinthian’s Diary’ Museum of Mirth 59/2: Sunday got floored in groggy plight.
1838		‘Alfred Crowquill’ Seymour’s Humourous Sketches (1866) 44: ‘You’re drunk — drunk, Sarah, drunk!’ ‘On’y a little elevated, Jack.’ ‘Elevated! — floor’d you mean.’ ‘Vell; vot’s the odds as long as you're happy?’.
1933		‘William Juniper’ True Drunkard’s Delight 225: Our tippler may further be [...] floored.
1943		J.A.W. Bennett ‘Eng. as it is Spoken in N.Z.’ in AS XVIII:2 Apr. 89: A thoroughly drunk man is stonkered, floored, stunned.

2. exhausted.

1869

T. Taylor New Men & Old Acres 8: Lil.: I am floored after the ball last night.

3. (US drugs) heavily intoxicated by a drug.

2001

Newark Advocate (OH) 21 Oct. 5A/4: Floored: to be too drugged to dance.