I do have a suggestion for you, Elaine.

You have some risk factors for stroke, so these episodes may be vascular warnings (TIA) of the carotid or higher. IVIG carries a stroke warning for the elderly. The dizziness and weakness (inability to stand) are stroke warning signs. Lipitor has shown some stroke potential as well.

It might be helpful for you to keep a journal logging all events that led up to a spell. Mornings only? Upon standing only?
After a meal. Before a meal. Only when tired. After taking certain meds? etc. It seems to me your doctors should be evaluating this risk for you, but you are not mentioning a doppler or tilt table test.

I hope you find out what this is very soon, as 6 months seems too long to me to have these symptoms and falls because of them.