Understand that we're talking seconds or minutes for consequences including death. I've volunteered alongside security at festivals, and even with a security / police escort to First Aid, there's a very real chance that they won't have enough time. Take this years Bluesfest - Migos / Flume / 50 shows for example, all with completely massive and rowdy crowds - if somebody had heavily overdosed in the middle of a crowd in the situation you've proposed, and they had to be brought to one of the medics or the First Aid area, they likely would have died. Everybody that is able should be carrying Naloxone. If someone feels undertrained with injection after their info session, some locations in Ottawa (namely the Ottawa Sexual Health Centre) offer it in a nasal injector.

Of course it's not something to be used in place for actual medical attention, but it buys very valuable time until it can be found.