The medical term for this is called opisthotonus - the head bent straight back. There is another term for the head going wry at a lateral angle: torticolis. The first thing that came to my mind was Newcastle and Marek's as this can be one of the clinical signs. Here's what the Merck Veterinary Manual has to say about it Newcastle:
"
Onset is rapid, and signs appear throughout the flock within 2-12 days (average 5) after aerosol exposure. Spread is slower if the fecal-oral route is the primary means of transmission, particularly for caged birds. Young birds are the most susceptible. Observed signs depend on whether the infecting virus has a predilection for respiratory, digestive, or nervous systems. Respiratory signs of gasping, coughing, sneezing, and rales predominate in low virulence infections.
Nervous signs of tremors, paralyzed wings and legs, twisted necks, circling, clonic spasms, and complete paralysis may accompany, but usually follow, the respiratory signs in neurotropic velogenic disease. Nervous signs with diarrhea are typical in pigeons, and nervous signs are frequently seen in cormorants and exotic bird species. Respiratory signs with depression, watery-greenish diarrhea, and swelling of the tissues of the head and neck are typical of the most virulent form of the disease, viscerotropic velogenic Newcastle disease (VVND, also called exotic Newcastle disease), although nervous signs may also be seen. Varying degrees of depression and inappetence are observed. A partial or complete cessation of egg production may occur. Eggs may be abnormal in color, shape, or surface, and have watery albumen. Mortality is variable but can be as high as 100%."
Here is a great resource for avian diseases - Cornell University's Atlas of avian diseases with a photo of a chicken exhibiting the same clinical signs (from Marek's) as your quail has shown:
http://partnersah.vet.cornell.edu/avian-atlas/search/disease/502
