For several years now I have been having some problems I've never seen a doctor about. I know when someone stands to fast they kinda blackout but I've never seen someone react how it feels for me. When I stand not directly after but sometimes I walk 20 feet or so I black out to the point I don't know what is up or down its like I'm just floating in space and I get a feeling like my brain is swelling up and gonna make my head explode. I also don't feel anything. What concerns me most is since having roommates I've had people see me during this time that say I shake as if having a small seizure. I'm thinking it may be connected to another symptom I've had most my life but that doesn't happen at the same time, I also get sharp pains in my chest that last seconds also very extreme. The blackout part usually last around a half a minute.