This is just a thought in response to your question about drowsiness.
You can research it further, but if the ingredient from Hoodia (p57) stimulates the receptors on cells in the hypothalamus to supress your appetite, I'm wondering if this in turn sends a signal for the pancreas to stimulate insulin production therby reducing the amount of glucose that may be present in the blood. Low glucose levels cause drowsiness,lack of energy, and sometimes light headedness. The brain needs a certain level of glucose to function properly.
I wonder if your dosage is too high.
Just a thought.