The word rage comes through French from Latin rabies, "frenzy, rage, madness". The English word apparently went from rage "vehement passion" to the fixed phrase the rage meaning "the latest fad"; then the expression x is the rage was intensified by adding all, similar to the way you can add all to other things, like x is all messed up.
According to the Oxford English Dictionary, the oldest sense of the English word rage as used in the 13th century was "madness; insanity; a fit or access of mania. Obs. exc. poet." (sense 1a).
The sense of "a vehement passion for, desire of, a thing" (sense 7a) was already used by Shakespeare, in it oldest quotation:
1593 Shakes. Lucr. 468 This moves in him more rage...To make the breach.
1671 Milton Samson 836 Call it furious rage To satisfie thy lust. ns iii. 65 The rage which possesses authors to read their writings aloud.
The oldest quotation for the expression (all) the rage (sense 7b), "said of the object of a widespread and usually temporary enthusiasm", is from 1785:
1785 Europ. Mag. VIII. 473 The favourite phrases...The Rage, the Thing, the Twaddle, and the Bore.
1802 Monthly Mag. 1 Oct. 253/1 The rage for the dotting style of engraving...is on the decline.
I'm not entirely sure whether the quotation from 1785 already has x is the rage as a fixed expression; the earliest quotation for that is from 1834:
1834 Lytton Last Days of Pompeii I. i. 173 Sylla is said to have transported to Italy the worship of the Egyptian Isis. It soon became ‘the rage’—and was peculiarly in vogue with the Roman ladies.
At the same time, adding an adverb to intensify the predicate the rage was already in use:
1837 Marryat Perc. Keene ii, In a short time my mother became quite the rage.
And the oldest quotation with all is from 1870, although that may not mean much for its earliest use:
1870 Ld. Malmesbury in Athenæum 4 June 734 In 1776, the game of ‘Commerce’...was ‘all the rage’.
In 1940, the term was apparently thought of as typical of the period after 'the war', which is presumably the First World War:
1940 Graves & Hodge Long Week-End iii. 38 After the war the new fantastic development of Jazz music and the steps that went with it, became, in the comtemporary phrase, ‘all the rage’.
Context is key. That being said, in most cases, in American English at least, "How are you?" just means "Hello." Not even a formal "fine" response is required. It would not be uncommon to hear two Americans have this conversation:
Joe, how are you?
Nate, how are you doing?
or
Joe how are you?
Nate, good to see you.
If you want to respond to "how are you" by telling about your condition, you can, but it needs to be a very short response.
Joe, how are you?
Not bad, how about you?
Oh, you know. Sick of all this snow.
or
Joe, how are you?
Doin' great. I closed the Smith deal.
No kidding?
The person asking "How are you?" is not trying to probe the depths of your health or your psyche; he or she is just making polite conversation. If they really want to know something, they will say something along the lines of:
I haven't seen you in ages. What have you been up to?
or
I heard about your husband. How are you holding up?
Best Answer
I do not know whether this is correct and have nothing with which to back it up, but it is too long to go in a comment, so it’ll have to be an answer.
Personally, I would suspect that this is perhaps a usage that has spilt over from Hiberno-English.
In my experience, a more or less semantically void ‘at all’ is often used in Ireland as a fairly generic closing statement in questions (much like ‘right’ or ‘innit’ are used to make statements into questions). “Do you see him at all?” just means, “Do you see him?”. If ‘at all’ should be taken literally, it is sometimes doubled: “Do you see him at all, at all?”.
As far as I am aware (though again I’ve nothing to back it up with), the Irish usage comes originally from the way the phrase ar bith (meaning both ‘any’ and ‘at all’) is used in Irish, which differs somewhat from English ‘at all’. Overuse of an expression common in one’s native language when speaking a non-native language is very common, and this is originally one such case.
From these examples, where ar bith sometimes means ‘at all’ and sometimes ‘any’, it is fairly easy for an Irish speaker learning English as a second language to overuse ‘at all’, leading to cases where ‘at all’ really just means ‘any’, or even less than that (“Did you see him any?” is not a very natural phrase, and English would just have, “Did you see him?”).
Ar chor ar bith (which unambiguously means ‘at all’, never just ‘any’) in Irish is a kind of ‘doubled expression’ in sound (ar X ar Y), so once ar bith was fairly solidly identified with ‘at all’ in English, I suspect it was rather a simple matter of simply creating a doubled expression in English to match the Irish one, and ‘at all at all’ was born.
The doubled expression has not (yet?) made it into British English as far as I know, but I don’t think it far-fetched to hypothesise that the weakened and seemingly improper use of ‘at all’ is something that comes from Hiberno-English.