Child hearing voices after high fever

[mamakaren]

My son is almost 6 years old. 5 days ago he had a high fever (104) during the night. When I brought him to the doctor the next morning he could find no evidence of any infection and thought it was some kind of virus. During the peak of the fever during the night he was hallucinating, claiming to hear voices "shouting" at him. He covered his ears with his blanket and cried to "make it stop." He has experienced fever delirium once or twice before always associated with sleep and illness. I was also prone to this as a child.

What has me very worried is that yesterday morning while wide awake and fever-free for several days he told me he can still hear the voices/shouting "in the back of his head." He is no longer sick and I know he isn't lying because he calmly brought it up on his own while sitting with me on the couch. I asked him later in the day if he could still hear the sounds/voices and he said "now that you mention it, yes." He told me that once I remind him "it comes right back" Since this fever illness he has also been complaining of intermittent mild headaches.

What in the world is going on? Should I be worried?

My son has no physical, mental, behavioral, or emotional issues or diagnoses.

Thanks so much for any help/advice.