Probably gave him too much Xanax. That crap outta be outlawed. You could rob a bank and kill everyone in it and the next day, you honestly wouldn't remember it. I'm not saying that's what this guy is on but it dang sure seems like it.
We use to take Xanax for fun when we were young and wild. Y'all wouldn't believe how dangerous that drug is. Literally wipe your entire memory away and make you crazy drunk feeling.
It would not surprise me. Xanax has well documented amnesiac affects. Its the reason why so many people overdose on it because they forget that they already took it and end up taking a lot more than what they are prescribed, especially when drinking.