I've had a few experiences in my past that, when brought to memory, cause fairly large adrenaline spikes. Certainly, the memories increase my heart rate by just thinking intently about them.

In theory... couldn't you bring these thoughts to memory - at random? When asked about what you had for breakfast, for example. It would appear as an anomaly... But if you did that often enough, the interviewer couldn't trust the anomalies.

There's no magic to it, you just have to really not give a shit about anything really. In the context of the US government, they want workers that are first and foremost, resilient to manipulation. Historically, the biggest traitors in the country have been money-driven, hence the emphasis on identifying huge debt areas. Such debt can be leveraged against people easily. The other thing to consider is, do you think they want someone that's too honest? What about in the scenario that you're being interrogated by a foreign agency, you're telling the truth but you're sweating balls. A polygrapher can latch onto these signs and use them against you. And someone that's emotionless and doesn't really give a shit about anything good or bad? Pass the polygraph with flying colors, have fun swaying someone that can't be bought off nor exempts guilt.