The first time, I ran out of air (not a big deal because of no SPG, it was a usual evolution) but I was deep. I think "crap!" and head to the surface fast, until I realize I had not pulled the j-valve for the reserve, so l pulled the reserve and continued to the surface normally, and calmly.
Now I just assume I'm narked past 100', so I won't take any deviation from my dive plan, or any small issue lightly. I just don't want to be diving fat, dumb, and happy and be supprised, when something goes wrong, that I'm narked.
On the good side, I do love following down the deep blue sirens of the deep, but I have learned when to go home.
Bob