Damage to the vagus nerve is potentially implicated. Low vagal tone could mean anything, such as damage to the vagus nerve from other sources or stress caused by the illness itself, rather than the other way around.<p>The problem with a diagnosis of stress is that no one lives a stress-free life, and identifying triggers that have have possibly caused a stress-induced illness is a guessing game. Unless there is a clearly defined link or test that can pinpoint that the exact cause of an illness was stress induced, it should be a diagnosis of extreme last resort. You could send someone on a wild goose chase, what with going to CBT sessions, counselors and psychiatrists, only causing them more stress as their condition continues to deteriorate.