I've wondered about the long term effects too. I don't know for certain, but I gather from past comments that the reason that I 'slept through' from 6 weeks is that I stopped being tended to. I was in my own room and there were no monitors back then which probably didn't help.

I had big problems falling asleep until I had DD - now I practically pass out every chance I get - but when I was a kid I'd be up all hours of the night reading by torch light or talking to myself, and as an adult I'd get seriously frustrated at still being awake in bed at 2am. I was also a very clingy kid, and didn't like to do things on my own. That changed when I was about 15, I started becoming more independent. Honestly, my Mum didn't handle that well and we still have a somewhat strained relationship.

So, I don't know if you could say it's because I was left to cry, or because when I was practically grown up Mum wanted to continue mothering/babying me. It has made me wonder though.