So, because I’m guessing at least a couple of you are as curious about it as I am, here’s what I found about going south and west with a little quick research:
Wiktionary has this about going south, citing Christine Ammer’s The American Heritage Dictionary of Idioms:
The origin is unclear. Common belief attributes it to the standard orientation of maps, where south is the downwards direction. Alternatively, it could stem from a euphemism used by some Native American for dying.
Norwegian Wiktionary didn’t have anything about going straight west. However, the Norwegian language council has this (translation mine):
“To go west” has in English long been used about dying (or breaking). The origin is probably the frightening thought of ending up where the sun sets (possibly far out at sea).
Some sources instead mention that it is criminal slang for ending up at an execution site in West Midlands in England. That is impossible for us to judge. The Wild West in America can at least be ruled out, as such an origin would be known in the Anglophone world.
The idiom supposedly spread wildly during the First World War. It probably came into Norwegian through sailor jargon. Tor Myklebost writes: “Seamen never say about their deceased mates that they’re ‘dead’. ‘He went west,’ they say.”
Straight west is a natural extension of west in Norwegian, and has long existed in its geographical sense.
Previously, the expression was often that something went north and down in Norwegian. Down in Denmark, projects rather go down and home, and in the east ((TN: Sweden)), to the woods or to hell, which of course also exists here. They can otherwise go in the sink, or worse. Things can further go ad undas ((TN: Latin, to the waves)), to the devil, in the dogs and to pieces – if it doesn’t simply bust. There might not be quite as many expressions for things going well.
One recurring thread in the Norwegian one is references to the sea. I have in the past suspected that it had to do with that, as the sea is to the west for most of Norway. But by the sound of it, the idiom originated outside Norway and spread here via sailors.
Also worth noting is that both the English and Norwegian etymologies appear to possibly have to do with death. It’s worth noting that in several mythologies, west is the direction to the underworld, so maybe some influence there might have been involved too.
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