problem with falling over after i stand up. dr answer please!?

im 13 and in fine health condition. ive never done drugs or anything like that but every time i stand up after like sitting or laying down on the couch everything goes black and i feel like im falling and if i don't sit down i will normally fall. on more than one occasion ive hit my head off of a piece of furniture. i have a 28 degree curvature of my spine and i herniated disk in my lower back. i also get migraines and headaches very frequently. what is wrong me? can any of these other problems be associated with this? help i need answers. i wood like a dr.s advice!!!