Yup - if there's one place you don't
want to push yourself in; it's ukemi - plenty of ways you can get yourself kilt with a single error. My advice: Don't worry about learning breakfalls; just practice them slow and easy. Like anything; it's not the speed that's important, it's the technique. Build the technique; build your body's ability to perform breakfalls without thinking about them. You'll learn them much faster than trying to push/test yourself.