I am happy to report that it TOTALLY WORKED. So stoked, so happy to have not lost that great groove.
I started at a very slow pace and realized that any time I did 3 strokes to switch sides I would get a little short of breath. This allowed me to spend longer on a single side (usually 4 breaths) instead of my usual 2-3. Eventually my breathing and heart rate synchronized and I was able to sustain a switch every third breath. By the 30 min mark I was going full steam and happily sailed through to 70 min. Man that felt good.
2 insights from this so far:
1) my breathing cycle synchronizes well with a breath every other stroke (same side breathing). I think I have a very slow stroke rate. I decided to pick up my cadence when I did a 3 stroke switch (changing to breathing on the other side) and this seemed to help. This seems related to a recent post by Tom P. noting that his cadence seems to increase with less frequent breathing. Seems like we have an internal metronome related to our breathing cycles and need to get body motion to adjust.
2) Also this is clearly related to my overall improvement in cardio health. I noticed today while going up stairs that my heart rate quickly accelerated and I was breathing too hard to simply exhale through my nose. I don't have a HRM with me but I am sure that I am encountering that really high spike at the start of a workout (been as high as 230 bpm) for me before it settles into a 138-154 average. In a terrestrial workout I don't really notice this because I can pant and gasp my way through it. In the water I can't ever break through that kind of spike because I just can't exhale quickly enough. Hence the need to ramp up the BPM slowly.