I only very infrequently co-slept with DD1 (maybe a dozen times) as she was in a moses basket then a travel cot when she was little and it just wasn't that convenient (I'd go to a different bed/room). However for DD2 I made the "mistake" of buying a co-sleeping cot as I didn't really like the moses basket for DD1, it was noisy, awkward and outgrown in no time ( it's not really a mistake - I think it's great)
DD2 is now 5.5 months old and generally apart from the odd time here and there where she has slept right next to me, has been happy enough to be slid back across to her own cot space after feeds and isn't disturbed by it. For a couple of weeks now though, she has been going through a development leap/sleep regression and she is waking more frequently and will not go easily back to sleep, unless she is lying on my arm (i.e. my upper arm is beneath her head/shoulders as a sort of pillow). It's the position that we naturally seem to end up in at the end of a lying-down feed and unless she's deeply asleep it's difficult to extract myself easily from this position once I am in it. Very often when I try, it wakes her up again. So, for a quiet life I let her stay and I love the snuggles
My concern is this: is this position going to cause her back/neck problems? She seems perfectly comfortable when she's there, even when awake. (My arm is more soft and pillowy than hard and sinewy!) Secondly, after a while, I tend to get a bit of a dead arm as although she is rather tiny for her age, 13lbs leaning on my bicep cuts off the circulation a bit. Am I going to give myself a thrombosis or something?!
Hopefully things go back to normal soon, not that I mind it though a bit more sleep would be nice, but I am going back to work in a few weeks and hope to also move her into her own room, if she'll let me!