By definition, the "common faint," or vasovagal syncope resolves rather quickly once the person is horizontal and blood flow to the brain improves; this can be hastened by elevating the person's legs (as most commonly it is blood pooled in the legs that is causing the drop in cerebral perfusion).
For a person to be unconscious for an hour or more, something else would be occurring. I can't even begin to speculate on what that might be because there really are very many different possibilities. I can say that you are most likely looking for something either neurological or cardiovascular/electrophysiological.
I can also give you an example of a scenario which could cause this; I had episodes like this myself when I first had my dysautonomia onset and it took years to tease out what was occurring. Please understand I am not at all suggesting that this is the cause of your daughter's episodes! I am only illustrating that all sorts of rare/bizarre circumstances can conspire to cause a medical phenomenon so as your daughter's medical advocate, it is important that you are the devil's advocate against what doctor's are taught in school ("when you hear hoofbeats, think horses not zebras"). I am a two-headed zebra: my long, sudden spells of unconsciousness sometimes had two combined causes, namely my two rare diseases. I have narcolepsy with cataplexy and generalized dysautonomia. As such, it's possible for me to faint and then go into a cataplexy (paralysis attack) from startling upon waking up, or to faint and then fall into a sleep attack from the narcolepsy and not wake up for an hour or more.
Now that I take medications for the narcolepsy, I don't tend to fall asleep when I faint, but there were times when it happened before meds. But before we teased out these two diagnoses, many other things were considered. My guess is that doctors will want to rule out epilepsy in your daughter. If the spells are several hours long, it could be status epilepticus, which is a serious medical emergency. Have you taken her to the emergency department while she is unconscious?
I suppose I should ask, just to be sure ...
When you say she is "passing out," what exactly do you mean? Does she suddenly collapse or is it gradual? Does she express that she feels any symptoms before it happens to warn her that it's about to happen (nausea, dizziness, changes in vision or hearing, changes in smell or taste, feeling overheated or chilled, headache)? Are you able to rouse her at all during these multiple-hour spells, either by calling her name or touching her? Is her body stiff or limp during the spells, or does it vary? Have you called paramedics when this has happened before? If so, did they try smelling salts to rouse her? Did that work? Did they try sternal rub (rubbing her chest vigorously with their knuckles)? Did that work? Did they lift her eyelids and examine her pupils? Do you remember what they said about her pupils?
If you can give more information, I might at least be able to tell you what type of specialist is your best bet at this point.
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