In Zeman’s original paper, the Vividness of Visual Imagery Questionnaire (VVIQ) is used to evaluate the quality of the mental image of 21 self-diagnosed and self-selected participants. This questionnaire invites the person to visualize a series of images (a relative, a rising sun, a shop they know, etc.) and rank how vivid the image is, from “perfectly clear and lively as real seeing” (5 points) to “no image at all, you only know that you are thinking of the object” (1 point). A total of 20 or less across 16 questions qualifies as aphantasia.
Aphantasia - Wikipedia
You have aphantasia.