it has happened to me that ive become lucid in an unpleasant dream and tried waking up but was unable at and other times its easy. Its nothing really to be scared of though because whether you like it or not your body is gonna wake up like normal in the morning - even if the dream lasts thats just the way it goes so i dont understand what you have to worry about.. i find when i cant wake up from a dream its because im actually not trying to, only thinking about trying to if that makes sense.