Toxic co-workers. They make every moment at work a miserable experience.

Their nitpicking ways, controlling and self-centered behavior can send anyone's anxiety and stress levels soaring.

Neil J. Lavender, a forensic psychologist, knows the type. He would lie in bed, talking with his wife about a former colleague at 3 a.m. "I would dream about him," said Lavender.

Now Lavender, 54, and psychologist Alan A. Cavaiola, 52, a professor at Monmouth University, hold seminars at companies about how these employees cause problems at work. They have written a book, "Toxic Co-Workers: How to Deal with Dysfunctional People on the Job."

Employees are more stressed out by troubled colleagues than they are by a heavy workload or salary concerns, Lavender said.

"If you are working with people who are out to get you, a boss who is out to do you in, that is when the stress is greatest," Cavaiola added.

In a survey of about 1,200 people, the two authors found that 87 percent had worked with a toxic co-worker at one time. They came to the conclusion that a good portion of the stress at work is caused by co-workers.

"It's like erosion," Lavender said. "Every day they wear you down a little, wear you down a little."