has he slept since he ate that brownie? if not, the sleep deprivation will make it worse for sure. in the worst case, get him to the ER and ask for something to put him to sleep. hopefully he will be okay when he wakes up. what he describes sounds like derealization to me (i had a DR episode a few weeks ago and that was fucking horrible. thankfully it has gotten already better, and i can manage low doses of alcohol and kratom but have stopped all psychedelics including weed for now, and probably won't touch them for many months so my mind can clear up). but don't worry, he probably is not going to be insane. i thought so too, when my DR started, had panic attacks and stuff like that, but you can manage it.
i know it already happened, but in hindsight, giving a first timer an edible wasn't a smart move. i remember when i smoked the first time, a few puffs of a weak joint got me high as fuck. CEVs stronger than LSD and strange but enjoyable audible hallucinations and stuff like that. with no tolerance, weed is a very potent psychedelic in my opinion.