Whew, ready through it all, took awhile.
It's a hoax of course. The "journal" is not written in the correct format, it's written to be a novel.
Also, the old suspense tool of haven't cameras mysteriously fail is used.
His first injury of hitting his head wouldn't put him out so much, even if it did split his scalp. I'd sure it would hurt like a bitch, but not enough for you to be incapacitated.
His second head-bashing inside the cave doesn't pan out. Protective helmits and hardhats have webbing inside of them to keep the actual help out of direct contact to your skull, hitting his head while wearing one surely would give him the massive back and neck trauma he claimed.
That's what I get from critically reviewing the text, but you want to know what surely makes it a hoax? The guy mentions the Hodag as part of his research. The hodag is a joke monster created by Gene Shepard. It's supposed by be about the size of an alligator that only eats white bulldogs and only on sundays. It's a joke monster that serves as a mascot amongst cavers. The mention of the hodag in accordance to his internet surfing is a clue for the reader to laugh it up.
Funny find though, I love deciphering these "internet accounts".