Well there is a man called Clive Wearing who has a 7 second memory, he still believes he's been "dead"/unconscious since he's illness in 1985, every 7 seconds even when they show him videos of himself from earlier in the day or things he's written down he doesn't believe it's him he believes the 7 seconds he's in is the true first conscious moment he's had, he even keeps a diary and writes the time he truly believes is the first time being conscious it's filled with multiple entries spanning decades.Whats interested he still retains knowledge of the world and other things but he has to be "prompted" in the right way to get that out of him, the only things he seems to remembers truly are some personal details like his wife, home telephone, family members and how to play music as he was a musicologist before he's illness but no true memories of any sort.His family don't seem to think he's conscious anymore they talk about being stuck in loops with him saying the same things over again and that even though there are elements of his old self there it's just bits and pieces the person he was is not there any more, even in the documentaries about him he says the same things over and over again the only change seems to be he's mellowed out about his condition as he used to get aggressive when he was discussing it with people.

There are 2 documentaries about him made decades apart

Prisoner of consciousness: https://youtu.be/aqiw2nx6gjY?si=hcapsCRBf2DxYIbF

The man with 7 second memory: https://youtu.be/k_P7Y0-wgos?si=jLjJ5JPSzB-UhuSI