For About 2 Days, On And Off During The Day

For about 2 days, on and off during the day and night, I become so hot I can't stand it, all over, become dizzy and light headed, then after a minute or two, I break out in a heavy sweat all over and am freezing cold and chilled, and my head feels like I have spun around in circles over and over many times and feel very weak. Any ideas what might be causing this? I have high blood pressure, which I take medication for, low thyroid, and had a hysterectomy about 7 years ago. Thanks for your help.