In one of the other "tips" in that video series, the author states that the tray tables are almost never cleaned between flights, and suggests wiping your own with a sanitizing towelette before use. Is this true? (Interestingly, this same author seems to have no problem handling the TV remote in his hotel room.)
But after fainting on two separate BA flights (747 SFO to LHR) years ago, cabin attendants on the second flight stated that higher-than-normal CO2 levels were not unusual and sometimes affected them the same way. In my case, both episodes occurred not long after completing the meal service, and involved a very modest amount of alcohol.
I would not be surprised if the dryness of the cabin air -- and what prolonged exposure to that does to nasal passages and throats -- were a contributing factor to coughs/colds. I guess one could consider using a face mask, as many people routinely do when walking around in places like Tokyo.