I agree with Randy and Gillian, so I'll add a little more about "I am out of it". Just think about what could cause that (being out of it) - tiredness, stress, resignation or even drugs. Actually, drugs would be my first assumption. The whole thing is, saying you were "out of it" is pointing at an outside cause.
Just use "sorry, I didn't catch that", "sorry, my mind was somewhere else" or "sorry, I wasn't paying attention" if you weren't listening.