6 of 14

Difficulty concentrating

Psychomotor retardation can slow down a man's ability to process information, thereby impairing concentration on work or other tasks.

"Depression fills one with negative thoughts, almost like an intrusion," Klapow says. "You're slowed down and constantly thinking about negative things in your world. As a result it makes it very difficult to focus on anything."

"I describe depression as a form of reversible brain failure, Dr. Sussman says. "When you're depressed, it's like your CPU [central processing unit] isn't working properly."

Next: Anger or hostility