I could touch the ears of my palamino stallion, but if I touched just below on his left side he would toss and shake his head for several minutes. I had him chiropractically adjusted, his poll and jaw were out. He is much improved and his symptoms are less intense but I feel one or two additional adjustments will be required to alleviate all of his symptoms. Also, have your vet check for allergies. It can cause sinus inflamation, swelling and discomfort, particullarily if it is putting pressue on a nerve or has caused a fluid build up in the inner ear. Either of these conditions can cause head shaking with few visible causes. A very close friend recently had the same problem (serious headshaking to the point of being unsafe to ride) with one of her barrel racing horses. After many vet visits and lots of expense it was determined he had very bad allergie but only after ruling everything else out. He is recovering well and has returned to competition.