Why has my iPad lost all the music and movies!!

After updating iOS in the last few days (to 8.3 something), I just noticed that all my music and videos/movies which I'd loaded onto the iPad are now missing.

This also happened after the previous update, and it is absolutely infuriating..., going away on a 2 week holiday in a couple of days and had specifically loaded music and movies for the 14 hour flight!!!

Why is this happening..?!

Thanks.