I'm not sure about the Rehmannia but I recently took a dose of both pregnenolone and DHEA (orally, on separate days in VERY small doses) and experienced similar symptoms to yours. In what form did you take yours? Oral intake relies on the liver to digest the hormones and this may be a stress on the organ.

Hi. I am taking Rhemannia in a formulation from Dragon Herbs for yin deficiency. It helps a lot and it increases my blood pressure . It's called Profound Essence and Codoponsis and Zyphyius. Not sure about the spelling of the last one, but they were recommended for me. There are lots of others to choose from and I have since gotten some other ones. But anyways, they gives good energy, like a normal healthy person has. Never too stimulated, which I hate and have experienced before with other things. I do recommend!