Dear Dr. Date,
I know that couples in long-term relationships occasionally fantasize about unattainable partners, but my situation is freaking me out! About three weeks ago while my girlfriend and I were having sex, I was momentarily overcome by the bizarre image of being underneath one of my professors. I’m not sure whether this counts as a fantasy, though, because I don’t actually find this person terribly attractive (and so, as you can probably guess, I was immediately deprived of my erection). The first time this happened it wasn’t a big deal, although I didn’t tell my girlfriend why I was unable to perform. The same thing has happened four times since then, and the strain is starting to show for both of us. I’m running out of excuses, and I’m now hesitant to engage in sexual intimacy. What should I do?
— Disturbed Pupil

The term gendoloma is applied when a person fantasizes about a person other than the person with whom they’re having sex. This term only partly describes your situation because usually people fantasize about someone more appealing than their partner to reach orgasm more quickly. This is also referred to as allorgasmia. Both men and women often fantasize about being with another person. It is not uncommon for these fantasies to be unwanted in real life. They spring from feelings of guilt or fear. Ah, the allure of the taboo.
Your case is interesting because it’s actually stopping you from having sex due to the displeasing visage of your professor. My guess is that you’re probably just stressed out about something. It could be that the demands of higher education are intruding on the rest of your life. This stress could be from a specific class taught by your fantasy professor, or it could be that the professor is simply a symbol for the authority and pressure you feel coming from school.
The human mind has an amazing capacity for grotesque thoughts. Our imagination is what makes us intelligent, but sometimes that same imagination can come up with some really twisted material.
Chances are anything you’ve thought of is relatively normal compared to what others are thinking.
There is also the chance that you are having trouble with your sweetheart. Some source of stress or anguish towards your love is manifesting itself in the form of your professor. This pain could fee like something terribly profound and relationship shattering and out of fear you repress the thoughts only to have them spring up during sex. I think you’ll find, however, that if you calmly identify what part of your relationship is causing the problem and calmly start relating these issues with your lover, things will be OK.