Jo, if Tom has changed suddenly, not a click of the fingers but over a few days / weeks / months then it is more than just a bit of a worry.
It might not be a bad idea for John to explain what he is seeing to a mental health practitioner or even your GP. NHS
choices would not be a bad place to start looking for mental health helplines.
Tom's change might be something or nothing, or it could be a cry for help from his suconscious. It sounds like he needs the help of a friend.