conceiving, conjuring (up), dreaming, envisaging, envisioning, fancying, fantasizing, fantasying, featuring, ideating, imaging, imagining, picturing, seeing, visioning, visualizing

daydreaming, stargazinghallucinatingre-creating(or recreating), reflecting, reliving, reminiscingcontemplating, meditating, musing, pondering, ruminatingconcocting, fabricating, inventing, making up, manufacturing, planning, projectingforeseeing, prefiguring