Bad air/fatigue. It's the headache/mind-numbing effect you remember from walking into a poorly ventilated classroom or such. It's not hard to detect, especiall

Bad air/fatigue. It's the headache/mind-numbing effect you remember from walking into a poorly ventilated classroom or such. It's not hard to detect, especially if sudden or strong, but to reliably act you need to regularly train to judge actionable concentrations, so you remember the feelings/perception for the specific actionable levels.