I’ve been thinking about this a lot lately, because I’ve been watching videos from a man named Jake Haendel.
He worked as an executive chef and inhaled an unknown toxin, likely from recreational drugs, but possibly at work. He was subsequently diagnosed with a terminal degenerative brain disease. He eventually went into a state that appeared to be a coma for 10 months. However, he was conscious yet unable to communicate during that time. He uses the term “covert consciousness” to describe that state.
A sharp-eyed doctor noticed something unusual and then his life changed entirely. He’s made a remarkable 4-year recovery and his stories are fascinating.
So if my loved ones are ever in such a situation where I have any doubt, I guess I’ll ask for functional MRIs 
?