Combinations - GBL and Alcohol

[dave-o]

My sloth would like some more advice please.
First some background:

Slow Hands (my sloth) is quite a seasoned psychonaut. He is middle-aged and has experienced most "things".

He is now wondering if there is any real sense in the advice that one should not take alcohol with GBL. Before the mob bays "don't do it", let me expand on Slow Hands' thinking.

Slow Hands loves K. He can take large quantities of it (although he doesn't any more). Anything up to a couple of grams in an evening. Slow hands also loves a drink. He can also take legendary quantities of this (3 bottles of wine an evening, for example). He loves to combine the two, and has never had any adverse reaction.

However, when he tried DXM, he had an awful reaction with alcohol. But then, DXM is a horrible, nauseous drug on its own, right?

So what he is wodering is; is there a proper reason why GBL and booze shouldn't be combined? Does it make you nauseous, like DXM, or is it just something that people say (as it is with K) to be "on the safe side"?