What causes continuous lightheadedness?

Lightheadedness is most often a temporary symptom from a transient blood pressure drop when a person goes from a lying or sitting position to standing. There are a number of causes, such as dehydration, a medication side effect, anemia (low red blood cell count), a heart problem and a number of other situations. When a person has “brain fog” and just not feeling like the brain is functioning normally, he or she may describe it as continuous lightheadedness.