Unexplained fainting/passing out?

I go to school everyday with a 18 year old girl. She has been fainting for hours at a time for 5 years. They hired me because her fainting has become disruptive to the classroom and wanted to get her 'out' as soon as possible after an episode. SO i get the wheel chair, and then take her to the clinic and let her finish her episode. Most of the time they last for an hour, but sometimes shorter and the longest since I have been with her was 3.5 hours.
Since I have been doing this I have noticed that every day it seems as though something triggers it. It does not by any means look fake; but I find it hard to believe that everytime she has a test or Spanish class she goes down. The classes here change times everyday; so it does not always happen in the same time frame but it does ALWAYS happen when there is a test or boring class. She has been to the Mayo clinicand many other places and they all cant seem to narrow it down. Her blood pressure does drop. Ill add more details

When she goes down it first looks like a siezure with very miminal shaking or clinching... once she is settled it just looks like she is sleeping with little stiiffening(her body becomes stiff as a rock) throughout. But when she gets up she is completley normal. SHe goes to many doctors a week and I am just wondering if anyone else besides me thinks that this may have some sort of relationship to stress. I dont want to over step my boundaries, but the nurses here at school dont know her academic schedule so they havent noticed her doing this with a pattern.. should i keep quiet or should i tell the parents my thoughts.... NAy idea to what this condition is. Also, she has very little, if any, on the weekends and after school.

Any insight is appreciated... good answers will recieve a thumbs up and the best 10 points!

Since you are already aware that her condition is undiagnosed it would not be overstepping your boundaries to mention anything you notice to her parents. Who knows, maybe that is the one piece of information that will help her Doctors figure out what is wrong with her?

Yes it sounds like something with her nerves. I used to do it too and it was nothing, I would get so nervous over something that I would pass out. I would turn white and out I went. Never lasted an hour, only a couple of minutes but it was all nerves. Nobody has figured that out yet? Take her to a doctor that deals with the nervous system. I am sure they have some type of pill for it.

It could be stress or nerves and I think you should talk to the parents about this that way the parents can talk to her doctors about it.