blacking out

I wasn't sure where to post this so i figured blood disorders was my best bet :P
But over the years i black out, i did it a lot when i was a kid but apparently grew out of it but then in the last 4 years its dramatically increased. Usually i can feel it coming on, kind of like a migraine, but its worse.. I feel it in my stomach which is like a warning so i know to get to a safe place and then i get dizzy and my vision blacks and i wake up on the ground.. i've been told i have a mini-seizure when it happens. I've been getting better at making it stop when its about to happen though. Its at random times which is weird, once after a few friends had been smoking weed around me, once after i had eaten and was having a cigarette (the first time i was able to stop myself from blacking out.. but ended up throwing up which was a first), once when i was getting ready to go to school (first time i had been all alone when it happened, kind of scary because i laid down on my bed and woke up on the floor) and today i was able to stop it but it felt like i was on drugs or something because the cement like got bigger and then smaller and i was freaking out and got really hot and had to sit down and chug some water...

I am going to see a specialist next within the next 2 weeks since i'm going home and am able to get blood tests done but i just want to know if anybody has heard of this and knows what it could be? when i've talked to my doctors in the past they never seemed too concerned because nothing showed up on my brain scan but obviously since its so random and happens in completely different circumstances even when i've eaten and had lots of water or when i'm just doing nothing its very concerning to me... sorry for the longness of the message :P thank you.

[Bhupinder Kaur, MD]

Hello,
For syncope/fainting to occur, either the reticular activating system in the brain needs to lose its blood supply, or both hemispheres of the brain need to be deprived of blood, oxygen, or glucose.
So it can be due to fall in BP,hypoglycemia, dehydration and inadequate electrolytes in the body, postural hypotension(orthostatic hypotension),, blockage of arteries supplying blood to the brain esp. the carotids,anemia,vasovagal attacks or underlying neurological conditions(like MS and motor neuron disease)

Sometimes, there are partial or complete blockages in the arteries that supply the brain with blood.  These blockages can cause a temporary loss of blood flow (called transient ischemic attack, or TIA for short), or permanent loss of blood flow (called stroke; also called cerebrovascular accident).This can lead to impaired blood flow through these arteries and so dizziness. In such cases CT brain can be useful.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.