Five seconds of not breathing does not constitute apnea. Think about it. A low-normal respiratory rate of 12 breaths per minute would mean five seconds between one breath and the next, and that certainly isn't apnea. If the patient had been hyperventilating, that five-second gap could have seemed quite a contrast without presenting any actual threat.
Hyperventilating can cause something called circumoral cyanosis, meaning the area around the mouth can look bluish, or in the right lighting, even gray. Taking small, shallow breaths for more than a few minutes can by physically taxing and the patient would very possible work up a sweat.
The fact that the patient could stop and start this behavior at will (when asked to, when no one else was in the room); his ability to wander the halls, eat and converse with others; and his removal of O2 suggest a problem rooted in anxiety rather than physical pathology.
I DO question why the patient was intubated if the "apnea" lasted for only five seconds. Diminished level of consciousness is not the same as loss of consciousness, and if the patient resumed breathing on his own, why would the doc perform something so invasive and unnecessary. Even if the patient passed out, I would hope the doc would wait longer than five seconds to determine the need for intubation.
Hyperventilating blows off too much CO2. This, in turn, lowers blood pressure. If the blood pressure drops too far, the person can pass out. Even though his initial blood pressure reading was elevated, it may well have dropped after his lengthy bout of hyperventilating. The ABGs bear this process out, as you said his O2 level was fine but his CO2 was low.
I'm thinking you witnessed a good old-fashioned panic attack followed by a fainting spell. It doesn't matter if the patient was or was not intentionally manipulating the situation. The result would have been the same either way.
The treatment, as you described it, seems questionable, at best. Unless there was underlying pathology--contraindicated by the labs and other diagnostic tests--normal breathing would have resumed as the CO2 level built up in the patient's blood stream.
This is the flip side of the little kid who holds his breath and turns blue when he doesn't get his way. Breathing too much or two little can cause you to faint. But then the homeostatic drive kicks in and the body works to regain its normal balance. Intubating someone who is hyperventilating makes about as much sense as it does for the stubborn child. It is simply not necessary and introduces a lot of potential for more problems.