injury includes unconsciousness, hysteria, pain and any substantial impairment of bodily function;
It's an inclusive definition. We know that those things referred to are injuries, but we don't know what isn't. Is giving someone a disease (other than one referred to in s 19A) an injury? Maybe. Is a mental illness? I don't know. There is no requirement that an injury be construed ejustem generis with the statutory list.
The meaning of serious injury at s 15 is equally vague.
serious injury includes-
(a) a combination of injuries; and
(b) the destruction, other than in the course of a medical procedure, of the foetus of a pregnant woman, whether or not the woman suffers any other harm;
Reference to the old statute books (and interstate and overseas authorities) about the division of assaults into felonies and misdemeanours, bodily and grievous bodily harm, etc. may be of some assistance. Probably not. The Court said in R v Rhodes (1984) 14 A Crim R 124 [Brooking J at 12, Young CJ and Crockett J in agreement]:
Once the jury has been given the usual short definition of grievous bodily harm, it is not the practice, and would indeed be unwise (Director of Public Prosecutions v Smith  AC 290 at p.335) to attempt a more elaborate exposition of the meaning of that phrase. The law gives only very general assistance to juries in this regard. While some injuries are manifestly too slight and some injuries clearly sufficient to answer the legal test, there remains an infinite variety of situations in which a jury might reasonably take either view. R v Weeding is, in this respect, no more than a judgment on its own facts. The question is one of fact and no principle of law emerges from Weeding that can be used as a fetter in later cases, other than the obvious principle that a finding of fact cannot stand where there is insufficient evidence to support it.
In R v Welsh and Flynn (Unreported, Supreme Court of Victoria, Court of Criminal Appeal, 16/10/1987, Crockett, King and Tadgell JJ) the Court said, [Crockett J at 10, the other learned judges agreeing],
There is no exclusive definition of the word "serious" in the Act. It was left to the jury to determine as a matter of fact what injury or injuries in combination might properly be categorised as being serious having regard to the fact that the word "serious" is an ordinary English word, the meaning of which must be taken as well understood by the members of the jury. This accordingly required that it be left to the jury to determine as a fact whether the injuries as it found them to have been should have been properly treated as "serious" injuries.
There must, of course, be a stage in which it would be impossible having regard to the ordinary meaning to be given to the word, for any tribunal of fact to find that an injury proved to have occurred could be classified as serious. If the stage were reached where it could not be so categorised then, of course, there would be insufficient evidence for the jury to make a finding of an injury as being serious in such an instance. In that case, it would be for the Judge to remove the matter from the jury's consideration.
A determination whether a given injury or series of injuries can be categorised as 'serious injuries' in terms of s 16 of the Crimes Act will no doubt involve a value judgment. That judgment will in turn involve comparison between the injury or injuries in question alleged to be serious and an injury or injuries which would, according to ordinary human experience, be commonly regarded as slight, superficial or trifling and therefore falling short of being 'serious injury'.