Why do you think he would lose his memory or become sort of unconscious during his "episodes"? I don't believe the girlfriend stated anything like that. She said he would "hear voices". That does not indicate, to me, that he was losing his memory or going into some kind of unconscious state that he wakes up from later.
It's true it could have affected his temper or anger, especially if the "voices" were telling him to do things. We've probably all heard a lot of stories about murderers saying they were listening to voices that told them to do bad things.
I don't believe he lost his memory. He drove that van home in a short period of time, suggesting that he was indeed having some kind of episode because the friend also mentioned that he would not sleep for a period of time when these episodes would happen. That would serve him well driving that van across the country. IMO
This is quoted from the NYPost:
"Gabby Petito’s boyfriend, Brian Laundrie, who has also gone missing and is being sought by the FBI, suffered with jealousy and control issues and experienced “episodes” in which he would hear voices and not be able to sleep, Petito’s friend told the Daily Mail."
Nothing about losing memory.
Brian Laundrie was controlling, had 'episodes': Gabby Petito pal