to say the fainting incidents were faked to make it look like Obama was having people swoon over him.  Then, somebody came up with footage of people doing the same thing at rallies at which Hillary and Chelsea were speaking.  It's very easy to do if you're standing for a long time, especially in someplace that's crowded and a little warm.  I'm not sure why, but if you keep your knees locked while standing, it's especially likely to happen.  I don't know why having your knees slightly flexed would improve blood flow to the brain, but it seems to work.