Question about fainting. is it better be sitting up or lying down?

Lying down: Lying down may effectively prevent a majority of the fainting spells (the so called vasovagal syncope). A smaller number of fainting events may be from cardiac causes ( less than 20%) and these may not be prevented by lying down but they would not be worsened. And lying down will certainly minimize injuries. While lying down, make sure the oral secretions do not go down the lungs.