What Do Episodes Of Nose Bleed, Profuse Sweating And Blackouts Indicate?

Question: My nephew who is 25 has had spells over the past two years in which he gets a "feeling something is not right by he can't quite pinpoint it, followed by nosebleed, then hearing loss, then vision loss, with profuse sweating and then passing out. It happens randomly, comes on suddenly and recovery can take minutes to hours.

He also has a problem sleep. He falls asleep fine but is waking up after 3 hours and bizarre nightmares and not being able to sleep after that. He has had both a neurologist and cardiologist say -- we don't see anything in you at this time, everything looks normal,come in when you're having problems. I'm trying to help him even figure out what specialy doctor he should see. I suggested a sleep study for the night time problems, but I don't know what to tell him about his spells. I am concerned.

The following are things that I thought may be the issue. Please explain to me why each on does or does not fit:
Fainting (vasovagal syncope) Nose bleed doesn't fit with Fainting, but it does make sense that your blood pressure has periods of dysfunction. I'm wondering if the nose bleed is a high blood pressure spike followed by a sudden drop in blood pressure, making it a nervous system problem.

An intermittent heart arrhythmia could be the culprit as some arrhythmia can fluctuate blood pressure -- but I imagine would be hard to diagnose without a prolonged EKG study -- wearing a monitor for as long as it takes to have an episode.

Another possible cause would be a sudden drop in blood sugar -- which doesn't seem to fit on the surface, as he told me you ate adequately that day. However, my nephew had 50% of his small intestine removed as an infant due to a blockage. He now has problems when he eats too much food with excess bile and nausea. Is it possible that his pancreas sends out too much insulin and drops your blood sugar too quickly after a meal? That would make sense if the pancreas functions similarly to the gall bladder in responding to a full stomach or duodenum by excreting insulin.

My nephew's father had some sort of congenital anemia for which he had to have blood transfusions. I don't know if this could in any way be related.

Anxiety attacks are also a possibility -- though he didn't mention feeling anxious as part of the episode. Nose bleed as part of a an anxiety attack?

Finally he has problems sleeping. He falls asleep fine, but wakes up after 3 hours with vivid nightmares. The rest of the night he sleeps in 30 minute intervals interrupted with waking. He has a cousin with narcolepsy. And his grandfather had an undiagnosed sleep disorder either narcolepsy or sleep apnea or both. Could these day time problems be related to the problem sleeping?

Thanks,

XXXX

PS -- it is a very troubling problem as these attacks can happen any time, anywhere. He had once while walking on the beach, and fell down, and woke up 4 hours later. He had one once while working as a bouncer, and someone was trying to help him after he fell down, and he thought he had been attacked by the fellow and came up swinging. (he now has a desk job) I'm concerned it could happen while he is driving or in some other dangerous situation.