Hi Joanie,
First of all, congratulations on starting HRT! It can really change your life.

To answer your question, your reaction may or may not be due to estradiol. Estradiol does have an effect on the endothelium (the cells that line your blood vessels), and can, over time, reduce blood pressure, but I don't know if there can be an acute effect. I never had any kind of reaction like that. If you continue to feel that way, you should consider contacting your doctor.
With kindness,
Terri