I have a pillow like this one for my neck:
My atlas is out of place, and any strain on my neck over long periods of time (like when sleeping) causes me too have migraine headaches for up to 2 days straight. Luckily the pillow prevents that, but after 6 months or so you will most likely need a new one, because they loose their shape and become very uncomfortable.
I'm gonna go off topic for a second here, but about a week ago my mum came back from one of her nursing classes where she visited the ward where all the brain dead patients are, and one of the doctors there told her that if someones Atlas and veterbra below that (Axis I think) are both knocked out of place you will be brain dead. That scares the shit outta me because when I was born I had a doctor (who is now in jail for doing this to many others) who used to twist the head of newborns like a cork screw too birth them. Many of these kids grew up with headache problems because the doctor had dislodged one of the veterbra and the body had grown out like that, causing strian on one side. It takes years of therapy to get the bone back into position and even then it is still very fragile. Mine is still way out, which is pretty scary because if I was to knock my Axis out also I would be braindead.