This is my 2nd baby. The first would move only to snuggle up closer to me -- I'd often wake in the morning with his nose almost touching mine (once he even started nursing on my nose!). This one, though, has made me a little nervous almost from the start. I even went out and got a crib while I was pregnant because I had a feeling I'd need it -- and I didn't even consider one with my 1st (who is now 9 years old). We haven't set it up yet but I think I will today. We have been using a cosleeper bassinet occasionally (another thing I didn't use with my 1st) but not all night. He's basically been in bed with me from the start. (He also started sleeping 4-5 hours at a stretch from week 2, and now wakes to nurse maybe 2-4 times in 10-11 hours.)
My little guy will be 16 weeks old tomorrow. He was amazingly active in the womb (way more than my 1st). He rolled over on his own at 9 weeks and now he just won't stay on his back -- he flips right over, can do a little pushup, digs in his feet and launches himself off the boppy pillow if he's on his tummy. He's a huge baby -- almost 10 lbs at birth (my doula noticed from the moment he was born how strong he was - he could basically hold up his head in the delivery room) and is now probably 20 lbs. Wearing 12-18 month clothes.
I woke in the middle of the night last night to find him scooched over a good 18 inches from me on his tummy with his face mashed (I think, wasn't wearing my glasses!) into the rolled-up blanket I have been using as a bolster between the edge of the mattress and the wall. (not a fluffy blanket) I had just reinforced it before going to bed that night just because I had a feeling. I flipped him back over and he was totally fine, breathing fine (his head was off to one side), and he stayed nicely asleep until morning. Still, though -- my heart about stopped when I saw where he was.
Something similar happened a few nights ago too -- I woke to find him on his tummy facing away from me at arm's length. My first NEVER did this -- if he moved it was always closer to me, not farther away.
I love cosleeping, but all my instincts are telling me to put this baby in a crib until he can really get up and move well on his own. (At the rate he's going, he's going to be crawling by 6 months....) I am not looking forward to getting him out of it to nurse at night at all (I feel exhausted just thinking about it -- cosleeping has always allowed me to get plenty of sleep) but I am starting to lose sleep worrying!