According to Harold Wentworth & Stuart Flexner, Dictionary of American Slang (1960), this usage of "something" in the United States goes back only to the early twentieth century:
something adv. Exceedingly. 1914 "He just cusses her out something fierce." S[inclair] Lewis, Our Mr. Wrenn, 1914.
Harold Wentworth, American Dialect Dictionary (1944) reports variants from roughly the same period using the regionalism suthin:
1914 Maine, n.N.H. Current. 'He come a-skivin', suthin' des'prit!' = extremely strong hard, swift. ... 1926 s.w.Mo.–n.w.Ark. Ozarks. Th' baby hed th' pukes suthin turrible.
A far from thorough Google Books search finds numerous examples from the first decade of the twentieth century. From J.W. Moody, "My Quandary," in The Wood-worker (August 1903):
We resawed a few pieces of 1x8 mahogany, when the saw began to dodge or lead to the left. As the machine was vibrating something fierce, I shut it off and explained that we must have a solid foundation under the machine.
From E.S. Johnson, "The Age Limit," in The Atlantic Monthly (April 1904):
'I have served them faithful now for forty year, good times and calamities an' all, an' now they put me to shame! ' Then he sighed something awful.
...
The new boss, he went down with a gang of six men an' did n't dare to go away from the foot of the shaft, 'cause they heard the pillars goin' whit-wheet, chippin' something awful, an' chunks o' top-rock settin' the fans goin all they could stand, to get up some o' the gas outen the workin's.
...
There was three men on, two o' them burned something awful to look at.
From Dorothy Richardson, The Long Day: The Story of a New York Working Girl (1905):
"Oh, they just up and at each other like two cats, tumbling over a stack of them there white velvet necklace-cases, and bloodying up each other's faces something fierce ; and then Miss Gibbs she called Izzy ; and Izzy he fired them on the spot."
From Edith Nesbit, The Incomplete Amorist (1906):
"I hope you said as how we should miss her something dreadful," said Mrs. James anxiously, "Have another cup."
From "A Crack-a-Jack New Year's Resolution," in Trade: A Journal for Retail Merchants (January 8, 1908):
Oh, they loaded him up clear to the ears. How by saying a few magic words or something like that they could make hogs multiply something fierce, and how there was a hungry market for all that could be raised at a price per pound that would make the first year's profits $8,462.66!
From O. Henry, "The Count and the Wedding Guest," in The Trimmed Lamp, and Other Stories of the Four Million (1909):
Papa's very proud, and when Fernando wanted to give me several thousand dollars for my trousseau he called him down something awful. He wouldn't even let me take a ring or any presents from him.
Etymonline states:
Anal-retentive first attested 1957, in psychological jargon.
According to Wikipedia, which does a much more thorough job of explaining than I will, the term comes from the psychological work of Dr. Sigmund Freud. Freud postulated that the anal stage of development, or that regarding toilet training, could have a profound effect on the later personality of a child.
The term anal-retentive refers to the retention, in later life, of such behaviors associated with the anal stage. These behaviors include:
"orderliness, stubbornness, a compulsion for control".
The term to describe those people who reject these characteristics is anal-expulsive.
Best Answer
It's an evolution of other imperatives that could also be used to express surprise or disbelief, such as "don't joke around", or in slang "stop fooling" or "quit joshing". While these statements are commands, the implication is that the speaker believes he is being deceived in jest. If the listener were to obey the speaker's request, they'd stop talking, or "shut up", hence the introduction of the command as a similar expression of disbelief.