What Does Constant Fainting Spells In Females Indicate?

I've had several fainting spells when I've tilted my head back to reach a shelf or when I suddenly get up from the ground. Also, my husband has squeezed me to crack my back and I've passed out twice. It's only for a few seconds and then I'm fine. I do have low blood pressure and have had problems with varicose veins in my legs due to pregnancies. I'm not overweight but I've not been getting much exercise in the last two years since my twins were born. Please advise on how serious this is and who I should see if at all.