The false perception that a hat is still on your head even though it was recently removed. Typically occurs after having hat in place for extended periods of several hours or more. The perception is often strong enough that you may reach to remove or adjust the hat even though it is no longer there.
At dinner, after the game, the starting pitcher experienced repeated moments of hatsation as he reached for a baseball cap that was not there.
by Barnguy November 17, 2012