What is this symptom called, where I wake up in the night, and feel vibrations in my head, with a high pitched undulating sound that rapidly increases its pitch and then stops with a pop? Otherwise it felt a bit like waking up from an unpleasant dream. There is mild anxiety, but no terror or panic. Heart rate is not particularly raised (maybe a little). There is no sweating or shaking. I think this is somehow related to low blood sugar, because not eating enough carbs makes it much more likely to occur.