The main thing is that if you feel like you're going to faint, get horizontal as soon as possible. Sitting on the ground is a lot better than sitting in a chair

The main thing is that if you feel like you're going to faint, get horizontal as soon as possible. Sitting on the ground is a lot better than sitting in a chair, but lying on the ground is even better and may avoid loss of consciousness - so even if your blood pressure is low for a few seconds, it's still enough to perfuse your brain if there's no hydrostatic gradient. If someone passes out in a chair, try and gently lie them down on the ground (obviously assuming it's a safe place...) - I've had a few patients who passed out in an airplane seat, and they are often out for much longer with much slower recovery than those who just crumple to the ground and end up horizontal.