"I feel spaced out" or "I'm spaced out' is a common expression for that. It could be any reason - lack of sleep, mentally exhausted, stressed out. You could just say, "I'm out of it" which is one of your suggestions. 'out of it' in this context means physically/mentally you can't do any anything close to what you would normally be able to. It's *usually* more about the 'mental' side, but there is a suggestion you may be very tired or run-down physically. "I'm in a trance" only has a mental component. It doesn't suggest any physical shortcoming or problem. It's just saying you can't think clearly.