Though I hadn't considered it in terms of cognitive functions, it's something I've noticed for years... when you're sleep deprived, or mentally fatigued in a similar way for any other reasons, do you find yourself deeper in your own head, and notice that your Se is weakened ?
On the particular day I was struck by the thought, for instance... the air was cool & crisp, I'd already been running for a couple miles at a solid pace, in nature, shirtless- conditions that would typically be conducive to a "clear" head. Nonetheless I found myself struggling to take in the details of my surroundings with the vivid sort of perception I like to when alone in nature. I'd had little sleep the night before. Certain times I am a very keen observer of vegetation, geography, etc & find it a stimulating game of sorts to be as mindfully present as possible in my observation. But other times, like on that run, I basically felt like an abstract, floating ball of Ni. My very conscious efforts to take in my surroundings were met with cloudiness and an inability to focus in a clear way.
It's dawning on me as I write this that obviously lack of sleep impairs the ability to focus in anyone. But I'd suspect from my own experience that INFJ's may be more prone to a rather insurmountable withdrawal from reality under said conditions. I suppose logically Se would be the first function sacrificed when cognition is weakened... But I'd propose that my "kinda tired" brain would lose in a test of Se to a hungover sensor who'd been up for two days.
Anyway. This is a dynamic particularly of interest to me as I've concluded time after time that optimizing my Se is crucial to my creating a reality that's in harmony with my intuition, imagination, and subconscious. Any thoughts on any element of this stuff are very welcome...