It looks to me like one of those newfangled blends, like craptacular, only this time the crap- is attached to fabulous instead of spectacular.
But, given that I found it in Proust, that analysis is somewhat unlikely. I know of a word, crapulent, of which our word could well be a sibling, that I think means 'drinking too much,' but I'll have to look it up. Oh, how I hate to look things up!
Yep, crapulous and crapulent are indeed brother and sister in meaning ' sickness caused by excessive eating and drinking.' My source is AHD4 as usual. It does seem meet that overeating would make one crapulous.
Now for the part I really hate: the etymology. This crappy word comes to us from Greek kraipale by way of Latin crapula which meant intoxication. But, get this, the Latin toxicus meant poison for arrows, finally explaining to me why the word toxophily, which means archery, sounds so poisonous. Toxon was the Latin for 'bow,' which they borrowed (no doubt at high and pointy speed) from Old Persian, in which it might have had the form taksa and would have meant 'arrow.' My search ends when I check a Farsi-English dictionary and learn that it lists the current word for arrow as tir, and I can but weep that our crapulous friend can trace his free-associative ancestry no further.