The specific TRPG replay video from page one is probably from this series, which even has English subtitles on youtube if you’re interested in seeing one of the more famous ones. (Watch at your own risk though, I haven’t seen most of it myself and can’t vouch for the content.)
I imagine most people are somewhat familiar with SAN points/Sanity checks at this point, but the “Idea Roll” in this context is a concept from earlier editions of the Chaosium TRPG. If you lost five or more SAN points at once, you’d need to make a roll against your Idea stat, and if you succeeded you fully grasp the horrors of whatever you saw and go temporarily insane (so, you actually want to fail this roll). “Temporary insanity” can be expressed in a variety of ways in the game, but one is simply fainting on the spot (potentially with more problems to come when you wake back up).
