What cause you to have hot flashes and then get real cold?

It depends. If you experienced menopause, this could be a " hot flash" , which is happens due to decline in estrogen after stopping having periods. Hormonal replacement therapy could alleviate the symptoms, but talk to your doctor to have a good check-up before it, especially regarding risk factors fof heart disease and stroke. If you are pre-menopausal, your reaction could be " premature ovarian failure" .