laying on back gets cross-eyed & flails arms/legs

[sienna tree]

So when I lay my baby on her back, she starts flailing her arms and legs and gets cross-eyed and is breathing a little faster.  When I get her attention or talk to her or hold her legs/arms down she is normal.  When I pick her up she is normal.  She's not crying at all, just moving fast and goes cross-eyed.  She doesn't ever do that when she is sitting up.  I also have noticed if I prop her head up a lot she doesn't really do it.  She's 4 months.  Anyone else see this happen?

[Just1More]

Sounds like normal reflexes to me.  She seems a little old for it, but not totally out of bounds.  Has she always done it?

Babies don't typically learn to converge their vision until around the time they start crawling.  So, when she goes cross-eyed, it might just be her trying to figure out where to focus and how.  When you get her attention, she has a focal point, and that stops the wandering.  As far as arms flailing, she probably just still has a startle reflex and feels scared on her back.  When you hold her arms, she doesn't feel like she's falling, and stops flailing.

Do you do well baby visits?  Might be something to ask your doc about, but I don't think I'd be too concerned just yet if it were one of my babies doing that.