Petra Boynton looks at research on feigning orgasms:

In a two-stage study respondents (all heterosexual women college students majoring in psychology) were asked when, why and how they faked orgasm. The researchers then narrowed this into four categories:

Altruistic Deceit (e.g. faked orgasm to make a partner happy or prevent them feeling guilty)
Fear and Insecurity (e.g. faked orgasm because they felt ashamed they couldn’t experience orgasm)
Elevated Arousal (e.g. faked an orgasm to get more turned on or increase the intensity of the experience)
Sexual Adjournment (e.g. to end a sexual encounter because of tiredness, a lack of enjoyment etc)

We tend to view faking orgasm as manipulative, whereas this research suggested that it could well play a positive role in increasing arousal. I could see an additional measure of distress being useful here to identify whether the faking was something done pleasurably to enhance sex, or an indication of other sexual or relationships problems where perhaps education or therapy might be of benefit.