Did you hold your breath during any of the exercises? No, but I focused on that.
Was it hard to find and engage your deep core? Honestly not, but I get used with it for some time due to other programs I already tested. Sometimes I'm not sure, if I overcompensate the deep core with the main abdominal muscles in a few situations.
Did your neck or shoulders tense during harder exercises? Not really, just in the end of rising arms I get a little reaction in my left shoulder.
Did you feel stiffness / pain in your lower back? No, but when my muscle strength drops, I tend to arch my back
Did one side feel harder to keep steady than the other? No, but the feeling in the right core is different to left (harder in tense, better controlled)