Low blood pressure can cause the dizziness and feeling like you are going to faint. I had that but was on blood pressure meds. I stopped the medication and this went away.
You should buy a blood pressure cuff. They sell them pretty cheap at Walmart. Keep track of what is happening. When you get up from a lying position, go slowly and then stand for a moment to make sure you are alright. I nearly fainted just bending over to get a pan out of a cupboard.
Definitely speak to your doctor about this. Perhaps one of the medications you are on can cause this. Have you talked to your pharmacist about it? They would know all about your meds...probably better than the doctor. Medication is their specialty.
Let us know what you find out. We really do care.
Sherrine