Thanks for posting the link! I've often said that my IQ drops at least 30 points when I stand up. My other joke is that gravity is my arch enemy.
For those who don't want to read the whole thing, this is a small study where CFS/POTS patients were subjected to orthostatic stress and then given mental tests. Here are two brief quotes:
CFS/POTS subjects' performance during the N-back task worsened as the level of orthostatic stress increased. The task performance of CFS/POTS subjects worsened further as the N-back difficulty increased but only during imposition of an orthostatic challenge. While supine, there were no differences between groups.
Specifically, working memory, attention, concentration, and information processing speed are progressively impaired as orthostatic and mental stress increases. This study also demonstrates that orthostatic stress impairs CFS/POTS subjects' circulatory, cerebral, and respiratory hemodynamics.