I'll take the middle ground here.
I can see the involvement of CO2 retention here. It can result from shallow/rapid breathing due to stress or anxiety or it can result when divers are concerned about depoth and SAC and artifically reduce their respiration rate to stretch their gas. The effect is the saem at both extremes - the diver does not ventilate well enough to effectively remove CO2 and CO2 levels rise.
The other factor here that needs ot be considered is that CO2 tself has narcotic properties at depth and eelvated CO2 levels exacerbate nitrogen narcosis.
In general, narcosis tends to axacerbate what ever the person's mental state happens to be. If the person is happy/content/etc then euphoria is likely to be a noteable effect. If on the other hand the person is anxious, then more extreme anxiety possibly leading to panic can be the noteable effect.
This is of course on top of the diminished judgement, problem solving skills and fine motor skills that accompany narcosis, and all of those can conspire to create stressful or anxiety producing situaions - mental states that are then exacerbated by the narcossis, so a 'good' dive at depth at high ENDs can go really bad in a really short period of time.
I agree with Dennis that everyone is going to be narced at 26m, I'm not sure "very narc'd' is accurate in general, but I thin you'd see meansureable impairment in anyone. The difference here is that in an experienced diver, they have enough mental reserve to meet the demands of the dive. However for a new diver with limited recent experience with equipment issues, and an 85' END exacerbated by elevated CO2 levels, "very narc'd" is probably a very accurate statement.
There have been times when have turned deep air dives due to the onset of even very minor feelings of anxiety as they can quickly get out of control, so if it happens, my advice is to immediately turn the dive and get shallower and re-evaluate the goals/purpose of the dive.
The same applies to trimix dives as some divers on some days may feel the effects of narcosis at ENDs in the 100-120' range and in some cases, some divers will feel the effects in the 80-100' END range. Trimix is not a magic bullet but rather just away to extend a givne END to a deeper actual depth.
In any case, the ability of a diver to function "adequately" at a given END depends on ther level of experience, the degree to which the fundamental skills of diving (precision buoyancy control, trim, gas management, situational awareness, familiarity and operation of all their equipment, etc) has been mastered to a degree where it no longer requires thought or attention but rather has become automatic, and the unique chalenges of the dive. For example, doing the same deep dive for 20th time on a familiar reef or wreck where navigation is not a challenge or concern in daylight in good viz, with a buddy and dive operator you trust is far less challenging than doing a dive where one or more of those factors are different. A deep dive for the first time in poor viz on an unfamiliar wreck or reef with an insta-buddy diving off a dive boat that is an unknown quantity, at dusk or at night where navigation is a constant demand will involve much higher levels of stress, task loading and problem solvijng abilities - possibly in excess of what you may have available at that particular END.
Recognizing that in advance and planning for a shallower dive or deciding not to do the dive is ideal. But if you are in the water, and feel the dive is getting outside your comfort zone, then you need to either amend the plan to stay shallower, or you need to turn the dive.
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In your case with only OW training, a small number of lifetime dives and a 20 year gap in currency separating you from that experience, going that deep should not have even been considered without several more dives progressively working up to that depth to gain experience, confidence and a better understanding of how you react at those ENDs. Adding in any equipment problem, such as a laking mask, is REALLY stacking the deck against yourself.
This is diving and while it is great fun, never forget people die doing it and 99.9% of the time those deaths are 100% preventable. So be prudent, think and never, ever do a "trust me" dive, even with an instructor. I'm a little biased and more than a little jaded, but in my experience there are far too many OW instructors who are compete and total morons. Trust none of them completely and develop the ability to understnad the issues and come to your own conclusions as you, not your instructor, are the one who wil be responsible for your safety and you will be the one dead if you get yourself in a situation from which you cannot safely recover.
I can see the involvement of CO2 retention here. It can result from shallow/rapid breathing due to stress or anxiety or it can result when divers are concerned about depoth and SAC and artifically reduce their respiration rate to stretch their gas. The effect is the saem at both extremes - the diver does not ventilate well enough to effectively remove CO2 and CO2 levels rise.
The other factor here that needs ot be considered is that CO2 tself has narcotic properties at depth and eelvated CO2 levels exacerbate nitrogen narcosis.
In general, narcosis tends to axacerbate what ever the person's mental state happens to be. If the person is happy/content/etc then euphoria is likely to be a noteable effect. If on the other hand the person is anxious, then more extreme anxiety possibly leading to panic can be the noteable effect.
This is of course on top of the diminished judgement, problem solving skills and fine motor skills that accompany narcosis, and all of those can conspire to create stressful or anxiety producing situaions - mental states that are then exacerbated by the narcossis, so a 'good' dive at depth at high ENDs can go really bad in a really short period of time.
I agree with Dennis that everyone is going to be narced at 26m, I'm not sure "very narc'd' is accurate in general, but I thin you'd see meansureable impairment in anyone. The difference here is that in an experienced diver, they have enough mental reserve to meet the demands of the dive. However for a new diver with limited recent experience with equipment issues, and an 85' END exacerbated by elevated CO2 levels, "very narc'd" is probably a very accurate statement.
There have been times when have turned deep air dives due to the onset of even very minor feelings of anxiety as they can quickly get out of control, so if it happens, my advice is to immediately turn the dive and get shallower and re-evaluate the goals/purpose of the dive.
The same applies to trimix dives as some divers on some days may feel the effects of narcosis at ENDs in the 100-120' range and in some cases, some divers will feel the effects in the 80-100' END range. Trimix is not a magic bullet but rather just away to extend a givne END to a deeper actual depth.
In any case, the ability of a diver to function "adequately" at a given END depends on ther level of experience, the degree to which the fundamental skills of diving (precision buoyancy control, trim, gas management, situational awareness, familiarity and operation of all their equipment, etc) has been mastered to a degree where it no longer requires thought or attention but rather has become automatic, and the unique chalenges of the dive. For example, doing the same deep dive for 20th time on a familiar reef or wreck where navigation is not a challenge or concern in daylight in good viz, with a buddy and dive operator you trust is far less challenging than doing a dive where one or more of those factors are different. A deep dive for the first time in poor viz on an unfamiliar wreck or reef with an insta-buddy diving off a dive boat that is an unknown quantity, at dusk or at night where navigation is a constant demand will involve much higher levels of stress, task loading and problem solvijng abilities - possibly in excess of what you may have available at that particular END.
Recognizing that in advance and planning for a shallower dive or deciding not to do the dive is ideal. But if you are in the water, and feel the dive is getting outside your comfort zone, then you need to either amend the plan to stay shallower, or you need to turn the dive.
----
In your case with only OW training, a small number of lifetime dives and a 20 year gap in currency separating you from that experience, going that deep should not have even been considered without several more dives progressively working up to that depth to gain experience, confidence and a better understanding of how you react at those ENDs. Adding in any equipment problem, such as a laking mask, is REALLY stacking the deck against yourself.
This is diving and while it is great fun, never forget people die doing it and 99.9% of the time those deaths are 100% preventable. So be prudent, think and never, ever do a "trust me" dive, even with an instructor. I'm a little biased and more than a little jaded, but in my experience there are far too many OW instructors who are compete and total morons. Trust none of them completely and develop the ability to understnad the issues and come to your own conclusions as you, not your instructor, are the one who wil be responsible for your safety and you will be the one dead if you get yourself in a situation from which you cannot safely recover.
) but the instructor had warned me about temperatures, so I had rented a hood. The other students thought it was ballsy but I had never been cold, of course I had never been past 80ft either, and our dive plan was "drop to or as clos as poss to 120ft, answer an easy maths question, and ascend". 3 students inc. me, instructor, and a DM. 
