Okay, okay, chill for a sec. Before he goes to explore this idea he needs to finish his thought from before. Where was he...
He sits back at the computer and starts typing into a blank document. It's easier to think that way.
Option 1: he's insane. If he's insane it's a very peculiar kind of insane, with other people interacting mostly normally and informing him that his contact list is indeed empty. But either way, he is hallucinating the preposterous state of affairs of having zero online presence in this day and age.
Option 2: he's not insane, he's not having any kind of mental breakdown, those people were not hallucinations.
...but does it matter? If he's having some extremely vivid dream or whatever, it's survived him passing out and then interacting with people. Maybe he's in a coma somewhere, but it...
...he can just act like this is real. When your hallucinations are this solid and strong and feel this real, clearly you can't use your own senses and pure reasoning to go back to reality. In the worst case, he'll be seen in public interacting with people and things that don't exist one too many times and the nice men in white jackets will take him somewhere.
Note to self: if you ever find yourself kidnapped by monsters or fairies or whatever the fuck else, consider the possibility that actually these might be the first real people you've interacted with in a while and your brain is just projecting your current elaborate fantasy delusions onto them. Be nice to them and try to find out if they can help you.
(However, do keep the possibility that this is reality in mind.)
However, on the off-chance that he can still somehow interact with the world, he can post something online asking if anyone has ever heard of symptoms like his. He'll go to Simmit and post a topic on s/NoStupidQuestions about it. ...and maybe s/MentalHealth too. Yes, that's good, he can check on these later.