Well,the only thing I can tell you is that this "差一点没" sentence doesn't make any sense to anyone.All you can and have to do is put it in your head. Actually,when I saw the sentence,like"我差点没被吓死",I was think of the thing as you do,"What does this sentence means". And I am a native Chinese speaker.So you see,some sentences in Chinese do not make any sense.But people just say it,say it and say it.And eventually it does make the sense.