Hi....I did answer some of these questions in your other thread -
http://www.medhelp.org/posts/Chiari-Malformation/Chiari-1-Malfunction-Bunch-of-questions-/show/2873402#post_13817537
With sleeping you do not want your chin down close to your chest......keep your neck from being bent which can cause you to block the flow of CSF flow....which is one of the reasons we have symptoms....it is a disruption of CSF flow....
Try to hold books or your computer monitor level with your eyes, again to avoid bending your neck to look down....this should help.
Tinted glasses can also be very helpful as florescent lighting bothers many with Chiari.
Proper posture is important and my Drs suggested I look into following Feildenkrais for proper posture.