Assuming that insomnia results from hyper-arousal of the brainstem arousal system, what can cause this? Presumably only excessive input from lower CNS levels. A prime candidate must be the vestibular system, which sends a lot of input into the reticular activating system and is heavily involved in sleep staging. To get to sleep, we need to lie horizontal and still. Hyperactive states of the inner ear are very common, and in this state the vestibular part is exquisitely sensitive to a very wide range of drugs. So I suggest that anyone with a sensitized ear (as with post-concussion syndrome, hyperacusis, autism, etc) will be over-aroused by many substances in the blood, as after overeating or having unusual foods before bedtime. There is a mass of circumstantial evidence in favor of this simple explanation, but are there any good arguments or data to rebut this theory?