Dizziness, which is what many people call a feeling of lightheadedness, is often due to a drop in blood pressure and blood flow to the head. This happens to me all the time when I get up too quickly from a seated or lying position, and happens to many people. This lightheadedness is called "orthostatic hypotension," which means decreased blood pressure related to changing your position from lower to higher. This experience can be normal, as it happens to me frequently, but it can also be a side effect of medications, dehydration, or other illness. When dizziness isn't momentary, one must be concerned about possible side-effects of medications, anxiety, alcohol, or arrhythmia -- a disturbed heart rhythm. Any persistent dizziness or a new feeling of dizziness that you haven't felt before deserves to be examined by your doctor. Vertigo feels like dizziness to most people but more severe, when you feel the room spinning aronud you. Some people get nauseated from being so dizzy, and it's not uncommon to vomit. Vertigo can cause such a problem with balance that some people can't even walk. Some people get vertigo from changes in head position (benign positional vertigo -- BPV) which often goes away, but some people have a viral infection, called "labyrinthitis." This can happen after a cold when inflammation affects the part of the inner ear that controls balance. If you feel dizzy when you get up too suddenly from orthostatic hypotension,you should sit down for a few minutes or even lie down if sitting doesn't make you feel better. After you feel better, sit up, then stand up more slowly. To prevent true vertigo from BPV, you should avoid changes in head position that bring it on which is usually one side more than another,and if it doesn't go away, ask your doctor for exercises that can make it better (Epley's or Sermont's). Lying flat often makes vertigo worse, so avoid that. Lie on an incline to avoid feeling more vertiginous.If dizziness or vertigo lasts longer than three days or if vertigo is severe, call your doctor. Other reasons to call would be any of the following symptoms:1.) headache, confusion, deafness, vision changes, weakness of arms or legs, or numbness anywhere; 2.) fainting or losing consciousness; 3.) recurring lightheadedness; 4.) a pulse of less than 50 or more than 130 beats per minute.