Jeanette, my Salmon Faverolle hen had the "exact" same symptoms, fine one day, on her side the next with her head and neck in the same position. Did she have the same disease/problem as your hen, who knows and with lots of care she lived, that was at least four years ago. Here is a picture of...
Probably nothing to worry about. But if you are, make a phone call and ask if there have been any Newcastle outbreaks since 2003.
"Check your flocks frequently for signs of disease, such as gasping, coughing, diarrhea or paralysis," said Dr. Hillman. "If birds are sick, or if there is unusual...
Forgot to mention that if possible, keep her upright on her keel, but if she can't/won't, left side is better, right side can put pressure on the crop and cause her to aspirate.
Jeanette, I know you said the vet is closed for the weekend, so does that mean you are going to take in on Monday?
Between now and Monday is a long time to go without proper amounts of water, so you should read this link on tube feeding...
From: From: http://www.harrisonsbirdfoods.com/avmed/cam/07_emergency_and_critical_care.pdf
FLUID THERAPY
Oral Administration
Oral administration is the ideal method of giving fluids.
This method is more commonly used in mildly dehydrated
birds or in conjunction with subcutaneous (SC)
or...
I had a couple of chickens do that. Both got better after 2-4 weeks and *lots* of supportive care (tube feeding). Sure wish I had known about BYC back then!