You know, Pen, I do regret not having another child for, among others, the reason that I won't get to see what it's like to be more relaxed with my second. Ed and I both just freaked out every time the least little thing was wrong (or so we thought) with Will, I moreso than he. I was like Shirley MacLain's character in "Terms of Endearment," running in to check on him when he was "too quiet" in his crib at night, and actually waking him once or twice accidentally when I couldn't tell if he was breathing or not and put my ear right up to his nose to make sure I heard air coming out of it. D'oh!
Your story reminds me of how a good friend told me once that her sister, the mother of three small children, had this to say about what it's like: With the first one, you worry about every little thing and fear constantly for their lives to the point that every time he or she cries, you're there in a heartbeat. With the second one you say "It's OK. Just let him cry it out. If he doesn't stop in five minutes, I'll go see what's going on." With the third one, you just turn the TV volume up louder to drown it out.
(Don't worry - she's an RN and a very competent and loving mother. Which makes the fact that she said that all the more amusing.)