Self-knowledge is so limited we sometimes get out own emotions wrong

This explains why it took the whole of Star Trek IV for Spock to work out the answer to a simple problem.

One day at graduate school, one of Lisa Feldman Barrett's colleagues asked her out on a date. She didn't really fancy him, but she had been in the lab all day and felt like a change of scenery, so she agreed to go to the local coffee shop. As they chatted, however, she started to become flushed in the face, her stomach was churning, and her head seemed to whirl. Maybe she was wrong, she thought: perhaps she really did like him. By the time they left, she'd already agreed to go on a second date.

Still feeling somewhat giddy, she got home, put her keys on the floor, and promptly threw up. It wasn' love, after all; it was flu. She spent the next week in bed.

Barrett's detailed analyses of the findings now suggest that there is no such thing as an emotion fingerprint. Each emotion may be represented by a whole range of reactions in the brain and the body, and there is a huge amount of overlap between each one. Instead, she points out that the way we interpret our body's signals - and whether we actually feel excited or anxious as a result - depends entirely on context and circumstance, and it can be easily shaped by our expectations.

Those few physical sensations – the churning stomach and flushed face – might have been (correctly) interpreted as ‘feeling ill’ if she’d been at home, in bed, with a thermometer in her mouth. But since she was on a date, her brain instead constructed an entirely different emotion – a genuine feeling of romantic attraction – from exactly the same physical responses. (According to the classical view, in contrast, the two feelings should have been easily identifiable thanks to their own unique fingerprints.)

A stomach ache, similarly, might signal a gut infection – or, if you were away from your family, might be confused with feelings of homesickness and longing. A rushing heart beat could be interpreted as fun and excitement on a rollercoaster, or acute anxiety if you are giving the speech at a wedding. Or it might simply signal that you’ve drunk too much coffee, but physiologically, there may not be much of difference.

And of course ghosts if you're, err, feeling Dickensian :

Because," said Scrooge, "a little thing affects them. A slight disorder of the stomach makes them cheats. You may be an undigested bit of beef, a blot of mustard, a crumb of cheese, a fragment of an underdone potato. There's more of gravy than of grave about you, whatever you are!"
http://www.bbc.com/future/story/20171012-how-emotions-can-trick-your-mind-and-body