But if you are brain dead, then you are not supposed to be able to think. If you get new memories from that time, where did they come from?
People that get restarted generally aren't brain dead. Generally they're heart dead (heart not beating) but the brain keeps clicking for a while after that (until the lack of fresh oxygen going to the brain because of the heart does enough damage that the brain stops). Brain dead is irreversible, heart dead isn't.