I only read about half the posts below, so this might have already been mentioned.
One thing would be to check your blood pressure. I know people with low blood pressure that are susceptible to passing out. Epsom Salts can lower blood pressure even more (dehydration, dialation), so this could be the culprit if you already have low BP (under 120/80).
Insulin and blood Sugar levels can trigger a pass out effect. Too many carbs, which we all eat before a flush, can send insulin levels soaring. Later your blood Sugar levels can drop dramatically.