knee-jerk reaction. Fig. an automatic or reflex reaction; an immediate reaction made without examining causes or facts. With one of his typical knee-jerk reactions, he said no immediately, citing some moral argument that no one understood. See also: reaction.
What did you see when the patients head was rolled to the opposite side? In horizontal canal BPPV, you should have seen a direction change. When the horizontal nystagmus is geotropic, the BPPV is suspected to be canalithiasis, occurring on the side with the more intense nystagmus.
horizontal field of view = 2 atan(0.5 width / focallength) where width is the horizontal width of the sensor (projection plane). So for example, for a 35mm film (frame is 24mm x 36mm), and a 20mm (focal length) lens, the horizontal aperture would be almost 84 degrees (vertical aperture of 62 degrees).