That's an interesting statistic. Don't really want to try it out, but interesting

But that means these whales are having the equivalent of their heads lopped clean off, and the state of shock may be preventing them from actually being conscious for those 20-40 seconds.

I think I'd side with Karl on the 30 seconds compared to a lot of other ways to go.
My wife's grandfather just passed away last Friday night. The last 6 months or so have been pretty tough for him and everyone around him. The docs kept giving him new drugs to "fix" problems that kept coming up. He's been mostly in pain for one reason or another. On and off for the last month or so he hasn't known where he was or who anyone else was. Early last week, they decided to take him off dialysis and to quit draining his lung that kept filling up. They gave us morphine shots to give him to make the drowning less painful.

30 seconds in the state of shock or 6+ months slowly...