Singaporean Missing in Greece - What Could Have Happened?

28 year old Singaporean medical student went to Greece for a conference. Didn’t show up for the conference, and has been missing for 2 weeks now. This is copied from the Facebook page:

What could have happened to him? If he wasn’t kidnapped, as they say, is it possible for him to have sustained a bonk on the head, not serious enough to go to a hospital, but enough for him to lose his memory?

Sounds like a Greek version of Paris Syndrome?

Hope he turns up safe and soon.

Mugged and killed?
Did go to an island and drowned while swimming?
Lots of possibilities.