Watch his body language closely. It's about the 25 second mark where he starts to feel something serious. He does appear to be *slightly* distressed from the start, but at 0:25, when the camera angle shifts, he is clearly beginning to worry. He knows something is wrong, but he's probably never felt anything like it before- ever have some weird ache or sensation you've never had before? And then it goes away, and you're like "wtf was that?", and it never comes back? I'd wager he was hoping that this was one of those. It wasn't. But as a professional, he ignored the lightheaded dizziness that was setting in and tried to finish his report. Blackness began to creep into the corners of his vision, his thoughts began to slow. And then his heart stopped, so his blood pressure dropped- suddenly his brain has very limited oxygen, so it shuts off all "non-essential" parts of the body- specifically, consciousness and control over your limbs. I know someone who OD'ed on heroin. They survived, because they fell over after shooting up and hit their head- this probably saved their life. They told me that as they began to realize they were ODing, they actually thought "You just killed yourself". I wonder if this guy had a thought similar to that flash through his mind just prior to him passing out?