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Indecision

"I can't count the number of people who have said, 'I had money in the bank but the phone got shut off because I couldn't bring myself to [pay the bill] or decide what to do and when.' It gets overwhelming," Dr. Cook says.

Some people naturally have a hard time making decisions, so an inability to make choices is usually worrisome only if it's a new behavior.

"It's an information-processing issue," and depression slows down your ability to decide, Klapow says.

Next: Suicidal thoughts