Why are we assuming he wasn’t doing drugs during the vacation? Obviously, he wouldn’t be able to hide doing like heroin, but if he does something like coke or pills or something, he could have easily just taken a bump or two here and there each day during the vacation and appeared to be completely normal. 

Not saying he’s not a POS, just saying, a lot of drugs are relatively easy to “hide” - and for most drugs, it takes awhile before your addiction gets to the point that you can’t hide it anymore.