Is this sentence same as "I get up"?
"I'm up" is commonly used in informal speech as a way of saying "I'm awake". As in this clip, it is usually used when the person is either surprised out of sleep or is trying to deny that they are falling asleep. The repetition of the phrase is simply used for emphasis to prove to that person that you are awake. Ex: A. Is my story putting you to sleep? B. No. I'm up, I'm up. Ex: A. Luke you need to get up for school. B. I'm up, I'm up.