Too much nighttime nursing?

( I don't think my original subject line was specific enough)

Michael Jude is 10 weeks now and still co-sleeping with us. I nurse him to
sleep each night as it seems to be the olnly way to get him to drift off into
never-never land. I'll deal with getting him to sleep on his own later on I
suppose but for now this has worked as a brilliant quick fix for a very
sleep-deprived, overwhelmed new mom.

Question: Last night DS spit up considerably twice. I'm not sure if it's
because I don't burp him at night when he drifts off to sleep OR if he's
overfed b/c he stays at the breast for so long. Even if he's merely sucking
for comfort doesn't milk still come out? Do babies know when they are full
even in their sleep ?

Thanks,
Lisa