Sorry to hear that you are dealing with dizziness
. I can give you some information about dizziness and my best guess as to what may be going on, but it does not replace the need to go get checked out by a physician if your symptoms persist. You are right in saying that low blood pressure can potentially be a cause of dizziness. There is something call orthostatic hypotension, which may be what is going on. When you are lying down, your heart does not have to pump against gravity to any great extent. When you stand up, all the sudden gravity is pulling your blood into your legs, and away from your brain.
It takes a couple seconds for your body to respond by sensing this, causing vasoconstriction (this squeezes blood vessels and increases blood pressure), and increasing the heart rate. In this lag time it takes for the body to respond, the brain (the most selfish organ in the body) isn't getting enough blood (and oxygen), so it makes you dizzy and will pass out if it persists long enough. Once passed out, you will be horizontal on the ground again, and gravity is no longer pulling the blood away from your head, and your brain is happy again. Any change within this sequence of events can lead to dizziness. (sensing the blood pressure change, the ability to respond and increase the blood pressure, or the inability to increase the heart rate, etc...) Of course there are other causes of dizziness that could potentially be contributing as well. Inner ear problems, problems with proprioception (pressure sensors in your body), etc. Orthostatic hypotension is just fairly common, and sounds like it may be whats going on by your brief history. Still I would recommend seeing a physician to get it checked out. Hope this helps.