IIRC (and not from Googling) it's because the blood's ability to accept and transport oxygen is dependant on the "partial pressure" of the oxygen, derived from the proportion of oxygen in the air (same at 370 as on the ground) and the ambient pressure(a lot less at 370). So, simplistically, the brain is fairly rapidly starved of oxygen, as the body was designed (or evolved) to function at normal Ts and Ps.
When I did my military flying training, we were decompressed while being invited to write names and addresses on a piece of paper. The "drunken" deterioration in the writing certainly confirms Mobius' theory of "useless consciousness".
And the beer and curry the night before could be quite noticable - even if it was the other guys who had indulged!!
