Not a mortal sin! The image you “saw” was dream generated. There is a brief period between full sleep and complete wakefulness. Since you fell back asleep so quickly, the residual memory of a dream is not within your control. It’s not as if you got up, relieved yourself, showered, got dressed, said your morning offering, and headed to breakfast, all the while concentrating on the “woman of your dreams” that you might dream of her again later that day or again that night.
Residual dream images sometimes occur when a person enters a brief waking period directly from REM (dreaming) sleep. If you think of the fictional woman again, distract your brain with another task. The devil is tempting you by getting you to worry about this. Another meaning for the word “worry” is to chew or gnaw upon, as in, “The girls peered through the fence slats and saw a large mastiff worrying a thick bone.”