Descent, often the easy part, went well and as scheduled, ascent went well up to the 200' stop and gas switch. Not having the gas I had planned, I had to reshape the plan with what I had, switched to intermediate gas and suddenly the world started slowly spinning. I work on the premise that:
If something feels wrong- it IS wrong!
Before I could switch back to backgas I felt a rushing feeling up and down my arms (I understand from a hyperbaric tech that was on my support team that this is not uncommon with an inert gas switch where the inerts are both relatively high in delta (He to N2 in this case). This sounds like it took an age, but in reality was very fast.
I returned to backgas, looked at my lost gas schedules and planned my next move.
I recalled reading Sheck Exley, in Caverns Measureless to Man, describe a procedure he adopted for a successful switch from a high He to high N2 gas and decided to give that a try. I wrote a quick note to my support diver who was watching me like a hawk and was right by my side as soon as I approached his stop- excellent chap to have around, he was clearly extremely well trained and knew his business (and I can modestly accept the credit for that!). It worked!
I often say that one must be a student of one's art or profession.
And I am very much the student of my art, as a technical diver. And being so may have just saved the day.