Music disappeared

I tried to play some music on my iPhone today and got the message "no content - you can download music from the iTunes store". Except there was music on it last night, and usage is showing as 30.6GB used (so the music is on the phone, it's just no longer seeing it as music). What has happened? I haven't upgraded anything since last night and have not connected my phone to my laptop. I have only charged the phone. I appear to have lost all my music and i'm thousands of miles from home and now having to contemplate the return trip with whatever music the airline can offer rather than my iPhone. Any help would be gratefully received!