So you are saying that you knew your life was dropping due to a bug of some sort, and you continued to test it till you died? I get the testing part, but you should leave important items behind when testing bugs.
My best guess is you had an invisible mob. You think someone dropped sand or something from the top of your ladder?
Flying has been known to throw players into blocks and suffocate them, but the death message should come as suffocation not falling to death. Maybe it was Herobrine?