In the previous post on using InSpectres to play JAGS Wonderland, I described what happens when Stress is higher than Unsanity, but I didn't describe how Unsanity increases from its starting level (0 for ordinary people, 1 for those already infected.) That's because there are several options, each with a different feel.
The simplest is: Unsanity equals the highest Stress level the character has ever had. If a character gains 3 Stress, Unsanity becomes 3 as well. If the character heals the stress, then gains 2 Stress, Unsanity is still 3. If the character then gains 2 more Stress without being healed, Stress and Unsanity are now both 4. This is pretty simple, but very hard on characters. Pretty much everyone would wind up infected if the universe worked that way.
Option 2: if Stress increases while being exposed to unreal or fantastic elements or events, Unsanity goes up by 1 point (and Sanity therefore goes down by 1 point.) Once infected, any kind of stress can trigger an Episode, but only the five triggering events previously listed can cause an increase in Unsanity. With this option, only the mentally ill and hallucinogenic drug users are likely to become spontaneously infected, with occultists coming in second. Other people become infected when exposed to those already having Episodes.
Option 3: players choose when to become more infected by buying off high levels of Stress with Sanity, perhaps at a 5:1 ratio. This has the benefit of giving players more control, but risks having no one becoming infected unless the GM rides the characters hard, hitting them with high stress rolls. The GM can also lure characters to the dark side by having a lot of NPCs with Wonderland-inspired abilities; in order to defeat the NPCs, the players may have to give in to Unsanity.