What sofiztk8ed said, and you're also likely to get halfway finished on one idea, only to decide that it's horrid, horrid, horrid nonsense that you hate and you'll want to start again and then panic that you don't have time to do anything good.
Really, anything can be made into interesting subject material. So try to avoid the freakouts (haha, impossible) and mind-changing, especially in the last month or two.
With enough preparation, you can be one of the rare ones who gets to sit back and laugh at other people having panic attacks and neglecting study to get their change-of-idea working.