According to Klein, Clinton is secretly facing "mounting health issues" that cannot be ignored.
Among her issues are "blinding headaches" that have "frequently plagued her," he claimed. As Radar reported, other insiders have claimed she has had a series of strokes and may be suffering from MS.
"For the first time I've known her, she's showing self-doubt about her strength and vitality," a friend told Klein.
Bouts of insomnia have "worried her, because it sapped her energy just when she needed it most for the campaign," Klein wrote.
The friend continued, "She is exhausted and depressed a lot of the time."
In fact, the friend claimed, Clinton even turned to sleeping pills like Ambien and Lunesta in her desperation, but they offered no relief. Said the friend, "She said they made her less sharp the next day."
As Radar reported, Clinton suffered a life-threatening blood clot on her brain in late 2012. Since then, Klein claimed, she has "constantly worried she was developing another blood clot…"
"There were incidents on the campaign trail when she felt faint and nearly swooned," he claimed. "Those incidents were kept secret."
For more stunning allegations from Klein's explosive book, stay with Radar!