after.
When the pain hits him he realizes he never particularly wasted a thought about his death. Not after the Horcruxes at least.
There had been the occasional frightening thought about running out of time, but none of them were ever grave enough to revive the terrifying panic he had as a child. Death had always been the cruel monster waiting at the end of his book. The punchline.
But now, in the end, Death is peaceful. Like the warm feeling of falling asleep after a long, exhausting day on Hogwarts' grounds. It greets him like an old friend that he hadn't seen in a while.
Perhaps if I would have known sooner, he thinks while falling, I wouldn't have been so afraid.