Feeding on demand and night time cues

This is going to sound dumb but for moms that feed on demand, what cues do you look for to feed over night?

The reason I'm asking is bec. in the very beginning, the Dr. wanted me to feed DD (now 2 months) every 3 hours. They told me to wake her at night to feed her until she got back to her birth weight. At night I wouldn't wake up until she stirred, which was sometimes 4 hours, so I would nurse her while she was basically still asleep.

I realize that I still do this but she may not be stirring because she is hungry. The one night she didn't stir, I was going to feed her anyway but I left her and she slept 8 hours.

Should I just be waiting for her to root? Will she root before crying if she is asleep?

Re: Feeding on demand and night time cues

DD always wakes up crying the middle of the night. She is 7 months now, but when she wakes up she always cries - sometimes she will stick her thumb in her mouth and fall back asleep, other times she will not stop crying until I feed her. They will always wake up in the middle of the night, so if she can just fall back asleep, I wouldn't feed her.