The word 'oblivion' preceded by the word 'sank' should naturally bring to mind a negative prehension, the conjecturization of an essense of the 'complementary' entities abstractly put as 'the container' and 'the contained' (which, ideally, should be sufficiently reduced to 'the uncontainableness', so to speak, in this case); thus, 'in' (as was used in 'into') should be eliminated to leaving only the 'to' behind (e.g., I sank to another level from where I previously got myself into), or if one chooses to keep it, the 'into' that is, just as it is, then one would simply add 'the' before 'oblivion.' On the other hand, something like the 'something' that passes into oblivion is logically and syntactically correct (vs. sinks into oblivion, where, the pre-existing verb-turned-quantifier 'sink', in this peculiarly particular instance, can not qualify for, or existing side by side with, the 'osmostic' nature of 'oblivion' because once one finds oneself in the oblivion, the mystery X-dimension of one's fated boundlessness that is, the magnitude of an oblivion's depthness generally becomes relative, if not to say indeterminable in most cases!) :)