Hi--did you also have an EEG to look for epilepsy/seizures?
And with the 24 hour monitor--did you have one of these attacks while that was on?
OK--then that pretty much rules out your heart as the cause here. While this could be migraine syncope, you still need the following
An EEG to look for a seizure condition
A tilt table test to look for autonomic dystonia--also known as POTS syndrome
A Doppler study of your carotids and vertebral arteries to look for any blood flow problems there.
Once all of that is done, if all normal, then the diagnosis of migraine syncope can be made.
Let me know if you need any more information here please.