Narcosis or Bad Buoyancy. Either sound possible from the description.
I agree. As far as buoyancy goes, I remember doing the Grand Turk wall earlier in my diving life and it can be disorienting to have no bottom and reference to the wall is not as easy as it looks. At least to me. It was easy to loose track of vertical axis.
I found narcosis is very manageable. First real experience was also on the trip mentioned above. Never been beyond 110 so a buddy and I planned a bounce to 130 just to see. As we crossed the 120 barrier the anxiety did increase and the focus narrowed. As a paramedic we gain experience containing our emotions and reactions so, to us, it was very manageable. Just focused on the task and put the anxiety on hold. Cleared quickly as we came up but we both noticed the change in our anxiety levels and had very similar eerily surreal feelings. I have since been over 170fsw on the San Francisco on two separate occasions. The first time was again anxiety provoking but not at 130fsw like before. The second trip I knew it for what it was and just enjoyed the euphoria. There was a ton of tunnel vision on all three occasions but I never had any loss of memory such as when on a major bender or when given pre-op medications.
AS NWGrateful stated, I suspect that the reactions are very individualized. If someone doesn't have a lot of experience in an altered state, (take that exactly as it sounds) then NN may very well be anxiety provoking. On the other hand, if in life a person has experience being altered, whether chemical, herbal or through highly charge emotional situations, then they should be better able to manage the symptoms. And as others have stated experience helps.
Just my theory. No attempt to validate made.