While nothing can excuse their behavior, not all celebrity meltdowns result from simple bad conduct.
Nearly 25 percent of Americans have been diagnosed with mental illness (with about 22 percent of them having a severe mental illness), and another estimated 22 million struggle with substance abuse [source: National Institute of Mental Health; Substance Abuse and Mental Health Services Administration]. And neither mental illness nor substance abuse cares if you're male, female, celebrity or an average Joe.
While some celebrity meltdowns are the result of ego or eccentricity, others are the result of something deeper. We've pulled together a list of famous meltdowns that may have had roots in mental illness or drug and alcohol addiction -- let's begin with Margot Kidder, the "Superman" star who fell into homelessness and rebounded as a spokesperson for psychiatric disorders.