Feeling sad or watching while receiving an injection may make pain an even more unpleasant experience, according to a pair of studies.
Pain is known to be a complicated mix of responses in the mind and in the body.
A study in Japan used different pictures of emotions to change the response to pain.
While a team in Germany showed that altering what patients could see also affected pain levels.
The first study, published in The Journal of Pain , showed pictures of sad, happy and emotionless faces to 19 people in the experiment. The pictures are supposed to provoke a similar emotional response in the person taking part.
At the same time as they were shown the pictures, the participants were zapped in the arm with an electrical current.
The painful jolt was the same strength each time, however, the people in the study reported higher levels of pain when looking at sad faces.
The researchers at Hiroshima University said: "Our results provide evidence that people tend to show higher pain sensitivities when they are feeling sad... and that emotional context is an important factor for understanding pain in human beings."
A separate investigation by a team at University Medical Center Hamberg-Eppendorf, in Germany, tried altering pain in a different way.
It replaced 25 people's left hand with a virtual one. A video of a hand was played on a screen and the participant's hand was placed underneath the screen so that it appeared as though the image was really their own hand.
The video would show either just the hand, the hand being pricked by a needle or being poked with a cotton bud.
An electrical jolt, which could be painful or non-painful, was delivered at the same time as the prick or the poke.
The researchers, writing in the Pain Journal , said: "Both painful and non-painful electrical stimuli were perceived as more unpleasant when participants viewed a needle prick, compared to when they viewed [cotton bud] touch or hand alone.
"This finding provides empirical evidence in favour of the common advice not to look at the needle prick when receiving an injection."