Why am i dizzy!! somebody help please?

i always have headaches an i think from stress i had a head cat scan an mri like a year ago an everything was normal i am 19 and weigh 130 and i am 5'7.. i dont smoke drink or any of that .. so i picked up a cl in school called tai chi which helps with balance an cordination. but today after really goin thru the excersises this morning in cl i got super dizzy when i left cl..like i cant keep my balance i feel like someone spin me around an now i tryin to get my balance an this started at 10:00 am an now its 12:30 an i still feel dizzy an not balanced ..is something wrong or is this common?