I think it depends.

DD wasn't putting on weight very well and I was told to feed her 4-hourly at minimum. I did think that she would wake up if she was hungry but what no-one told me was that if she wasn't generally feeding well, she might actually be too exhausted to wake up and end up dehydrated.

I certainly noticed that when I let her sleep five hours when she was about two weeks old. When we did wake her, she was obviously not her usual self - seemed very lethargic and just not right.

Having said all that, if you baby seemed fine after eight hours sleep and generally feeds well and there's no concerns about weight gain then enjoy the sleep!

But above all, don't feel bad - it was an accident and certainly won't cause her harm from just a one-off.