You are SOOOO not a terrible mother! Never say that!
Like the pp, my ds was in NICU beginning the day that we were to be discharged from the hospital. Though it wasn't to the extent of pp's situation.
I woke in the middle of the night to ds on his side with a foamy substance coming from his mouth. Within seconds of my going to the bassinette and aspirating him, I picked him up and he went from a healthy pink to blue in my hands. It is still a vivid picture in my mind that makes my stomach churn into knots and makes me cry (you should see me right now). I spent 4 hours in my room crying and praying, praying and crying that my sweet boy was ok. I'm so thankful that the post-partum nurse on duty was so wonderful in just giving me hugs, words of encouragement and best of all-went back and forth to NICU for me to get updates.
My poor son was poked and prodded for nearly 2 weeks until we found out he had reflux and PDA. His poor feet were spotted with needlemarks, he was hooked up to all kinds of machines and monitors (he also had apnea), but thankfully was the healthiest child in the room.
When it comes to your child, anything you do IMO is completely ok. I flipped out this morning because ds has been a little stuffy, and this morning he was having additional breathing difficulty when on his back so I immediately took him into the pediatrician. Turns out he has an upper respiratory infection which is hitting it's peak. He has to be clear of this infection because his PDA surgery is in 2 weeks. I'm happy that our ped and the nurses are so wonderful and accomodating, especially in our circumstances. I wish that all care givers could be that way, but we unfortunately can't count on that at all.
I am SO sorry that your experience was so terrible. Never second guess your gut instincts, and certainly don't worry about what the hospital employees think about you or what you ask. If their child was in the same situation, they would do the same thing, I'm sure. If you want additional testing done to make sure that your dc is ok, go ahead and do it. Don't let anyone discourage you or talk you out of it. YOU are the parent, not them. They don't have to worry about your child, they won't spend the sleepless nights ready to pounce at the first odd sound. That's what not only makes you a mother, but a phenominal one at that.