I had a very similar experience when I was around 8. High fever gave me a "rolling" feelin, as if I was a giant blob. My mom said I was grasping slowly at the air with my hands. I remember it to be a calm, pleasant experience, not scary at all. There was also an instance in which I floated above my body. I was in a hot air balloon floating above the exposed rafters in our home. I could look down and see every detail of our living room, even seeing myself lying sick on the couch. Again, I don't remember being scared, but just really "wanting" to come back down. Not sure if it was an hallucination or an out of body experience....I can remember it like it was yesterday. I'm 43 years old now.
I agree with babygirl your child was having a dream,it is possible that she saw something on TV or a book that triggered it off, is she at school/daycare that could also have been where she heard something .
I think there are times a baby can have a bad dream, convincing themselves it is real when they awake, with the fever she may have been so disoriented she believed her dream as she awoke. Tell us how she does when she is well.
Also Id suggest not bringing up the subject, she may get to playing along even when she has no more fever, because it is a way her imagination gets moms attention. Don't confuse this with outright lying, more like imaginative. In other words follow her lead, and don't make a big deal out of it unless she is truly scared in daytime hours