But experts are quick to point out that clinical mood disorders are not contagious per se.
Depression and bipolar disorder are complex, rooted in genetics and subtle brain chemistry. Experts point out that these disorders cannot infect people nearby the way a virus could.
"A depressed person will not give you the same clinical disorder by contagion. They're just too complex for that," said Ian Gotlib, professor of psychology and director of the Mood and Anxiety Disorders Laboratory at Stanford University. "It is rare that you yourself will develop that same psychiatric disorder."
But a person with depression or other disorder can have a tremendous effect on those around them. Studies on college roommates show that when one person has depression, the other roommate can develop similar behaviors and feel more down.
"It's not the mimicry, it's the stress of being around them," Gotlib said. "The mood stuff happens, but it's not clinical."
Coping strategies are critical when dealing with a depressed spouse.
"If the caregiver believes the behavior is caused by the illness, they are less likely to be affected," Galynker said. "If they think the behavior is the result of a character flaw, they are more likely to be affected because then they also place blame on themselves."
Carol Rossetti never thought she had a clinical condition, but she eventually became so unhappy with her husband that they separated.
"When I left him after 34 years of marriage, I didn't think we'd get back together," Carol said. "I was perfectly fine not being with him."
But Ron quit his job and went through therapy to get his disorder under control, and after a year of separation, the Rossettis came together again. Now both Ron and Carol know how to maneuver around Ron's episodes.
"The last ½ to two years have been the most worry-free of my life," Carol said. "Now he's a born-again bipolar person."