By the time the sun began to rise one recent Friday over his Mira Mesa neighborhood, Mitch Hood had been up for about 18 hours.

He punched a caffeine tablet out of a blister pack and washed it down with two cans of Red Bull. He finished it off with a gulp of Pepsi.

He figured this would keep him awake four more hours. Then, he jumped back into his video game.

Hood, 25, spent two tours with the Marines in Iraq. Now, like many other veterans and millions of civilians, he faces a new enemy: sleep.

"I'm afraid I'm going to have nightmares and I'm going to get stuck there," he said. "I try with all my strength not to sleep."

When he eventually crashes and sleep overtakes him, Hood relives combat, or sometimes his mind creates new horror-filled scenarios. Once, he punched his fiancee, Natalya Gibson, while having a nightmare. She insisted it didn't hurt, but Hood . . . (more)