Well, this post ignores a few points I and others made, such as:
- Nitrous oxide doesn't work that way.
- The episode would have to include a hallucination that is never, ever identified as such and has no discernible end-point (in a show that was fairly heavy-handed about telling the audience what to think and what was happening).
- McCoy would have had to not only hallucinate the settings of the holodeck but the technology that made it work, such as the "audio tapes rewinding."
- In fact, the computer would have to be confused, as it explicitly says that the "joke" in one scene is falling into a pit, not a hallucination.
How would the computer know what they're hallucinating?
I just don't think it's a likely scenario, especially as
hallucinations aren't even mentioned at any point in the episode--everything that happens is described as a technical malfunction. Therefore, surely the simplest explanation is that the malfunctions are technical. Anything else would be in realm of speculation, I think.
EDIT to add: For the record, "hallucinogens" are also not mentioned in the episode. After the gas makes everybody giggle, Kirk says, "Captain's log, supplemental. Somehow Spock managed to switch on our emergency air before collapsing from the effects of the gas. The fresh air quickly revived us, although it'll be exhausted in another six hours." And then we see the rec room holodeck still running. So...
But you do you. Enjoy.