My wife's original diagnosis was Alzheimer's, and it only came out a couple of years on - when I questioned it because of her vascular-type progression - that they said, well she has vascular dementia as well. These days she has about 3-4 faints a year that are detected. In the early days she might have 8 a night at the worst [but then I was beside her and awake all night awaiting them]. As with all things, the presentation of symptoms is different for each person. In the early days, the medics considered all sorts of possible reasons for the fainting - low blood sugar, arrhythmia, too much alcohol, etc. Of course it is always worth checking even the most unlikely out as any of them will be better than a diagnosis of dementia.