Experients in which are more likely than the average individual to experience such feelings as anxiety, anger, guilt, and depressed mood, typically score at chance or below-chance during psychical testing regardless of the psychical potential.  

Because they characteristically respond poorly to environmental stressors, are easily threatened, and fixate on, and describe, minor frustrations as being hopelessly difficult, they are less likely to score well because these characteristics are not psychically conducive.

However, if an experient with high levels of anxiety or marked reliance on defense mechanisms scored at chance, and later address and work through their anxieties (e.g. through behavioral therapy) the experient may then score at above-chance during psychical testing. This has proven true in my research; that individuals with acute or chronic mental illness report and exhibit increases in psychical performance quality after they have been successfully treated for the condition.

More Info About Psychic Experiences & Mental Health: Center for Exceptional Human Experiences