Yeah, I'm thinking it's the last option. He was in the water for 15 hours. If he were blackout drunk, the adrenaline would have worn off long before the alcohol did. He would have got sleepy and drowned. Same with the roofie.

I think the suicide or dumb stunt option is more likely. And I don't think it's necessarily that he's ashamed to admit it. It might be that he feels (or has been advised) that there could be legal ramifications for what he did, as far as the rescue operation goes. Or even something as simple as the cruise line banning him from future cruises might be on his mind. (He said he wouldn't mind going on another cruise, since he didn't really get to go on this one!)

So it might be a situation where he doesn't want to say anything so not to put himself in any legal or civil trouble. "I don't recall" is a classic answer from lawyers/politicians under oath, and that's essentially what he's saying here.