dizziness

  I am a 19 year old, otherwise healthy female who has been experiencing
  periods of dizziness for the past 6 months. It usually happens after I am
  lying down and especially after I have been crouching down, say to look at books
  on the bottom of a book shelf. When I stand up, I see large black spots and
  feel like I need to vomit for about 10 seconds. After that, i'm fine. I'm in shape,
  I take walks everyday, do yoga, etc. It's been more frequent in the past few
  weeks, like EVERY time I crouch down. Any advice you have would be appreciated,
  and I do plan to see a doctor if necessary when I go home in March for Spring
  Break.
  Thanks,
  Jessica

[CCF neurology MD MM]

_
Dizziness and blacking out of vision on standing up from a supine position
is usually associated with an inability to maintain adaquete blood
pressure.
This can be due to a variety of factors ranging  from anemia to inadaquete amounts of sodium
in the blood which in turn may be related to adrenal hormone deficiency,
or to inability of the heart to repond quickly to changes in posture.
There is rarely a serious untreatable underlying cause, however this does
need to be investigated as soon as posible and I would urge you not to
delay in having it checked.