The latter one is also accepted but i don't think it's widely accepted in formal writing. In a word, intentionally or accidentally? Dumbtionary (a dictionary of misspelled words).
Little Pesky Friends Cartoon by karynchan0306 on DeviantArt
True, accidentally is the correct spelling. The jury returned a verdict of accidental death 陪审团. Accidentally：没有附带性；完全出乎意料。 例句：i accidentally broke a glass.
Does this sentence mean 'you' intentionally tried to hurt 'yourself' or accidentally hurt 'yourself'?
So the regular construction would be accidentally. On the other hand, middle english used accidentlych as an adverb, and this would produce accidently in modern english.
