Panic and hypersensitivity to physical symptoms. "Are you tuned into your heartbeat?", post at the British Psychological Society Research Digest, discusses recent research into how different populations (people who are particularly afraid of anxiety-related symptoms, people with "normal" levels of fear of anxiety-related symptoms, and people who are particulary immune to fear of anxiety-related symptoms) interpreted "the sounds of either normal or abnormal, palpitating heartbeats against varying degrees of background white noise." From the post:
In trials containing normal heartbeats only, the more anxious participants were, as expected, just as good at detecting them, but crucially, they also tended to report hearing a heartbeat when there wasn’t one – far more often than the non-anxious participants did.
Less expected was the observation that the more anxious participants were actually poorer at detecting abnormal heartbeats – the researchers think this might be because the sound of an abnormal heartbeat triggered a fearful response in the anxious participants, thus compromising their performance.
Finally, given a mixture of normal and abnormal heartbeats, the anxious participants showed a greater tendency to mistake a normal heartbeat for an abnormal one.