There are a lot of us (including me) having the same problem and there are a number of threads about it. It seems to switch into YouTube on Safari with the last video that was posted to your wall (that is what is happening to me and other people have made the same comment). Whether it is related to the new 'timeline' feature on Facebook, or their rumoured new iPad app I don't know, but it's also been reported on Facebook's help site. Until ithey fix it you could access Facebook just from Safari on your iPad and/or from your computer