Breastfeeding at night question?

So here I am, a first timer - and I suppose I'd be asking my mother if she were on Skype right now, but she's not!

So the last couple of nights, my little one - who will be 4 weeks old on Tuesday - seems to have woken up much less frequently at night to breastfeed. Or I should say, when she sleepily wakes, it's actually quite hard to get her to breastfeed when she usually does - she just wants to go back to sleep. When she does, she doesn't seem to do it for very long before dropping off again.

This morning she awoke and was hungry, and sucked voraciously at my one side for about five minutes (I think - I was tired and dozing) and then...back to sleep! Here we are at 10.25am and she is peaceful as a little bug in a rug! We co-sleep so she's in the middle of the big bed, warm and sleeping like a log!

We did have a busy day yesterday - went to the next town, and had a friend come over for a mama-baby photo session in the afternoon, so from about 4.30 until bedtime she was mostly awake, and feeding a lot - despite my ideas about a nap she did not seem to want to sleep and was a bit fussy unless I held her in my arms.

But then last night, I got up to change her diaper after probably four hours of sleep and it was nowhere near as heavy as it normally is. Usually she eats and pees and poops all night long. This is just different, these last couple of nights have been unusually peaceful.

I mean, she's so young: should I be worried about this?

Thanks in advance!