Car seat sleeping...

Okay, so this is a question I had earlier, but forgot about until just now. Katy's pediatrician told me today to not let her sleep in her car seat because it could cause her to have a flat head. That just doesn't seem to make much sense to me...I mean, Keryn and Jenafer's kids all slept for a couple of months in their car seats, right? And they don't seem to have flat heads. Caren and Samuel, did Adam and Kip sleep in their car seats? I just wasn't under the impression that that's what caused that to happen. And Katy really does sleep sooo much better in her car seat. And I just got her on a schedule that's working, if I try to get her to sleep without her car seat, I'm scared that I'll just go back to not getting any sleep at all and I'm not sure that I can handle that. Anyway, so I'm asking for your opinions...should I follow the doctor's advice or just keep my happily sleeping baby girl in her car seat?