I’m tired is all.
How can I parse this?
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Sign up to join this communityIt's not a grammatically correct sentence by itself - usually it would be something like
"I'm tired" is all [that I want to say].
or
"I'm tired" is all [that's wrong with me].
It means that there are no major problems; the speaker is just tired, which explains their odd behavior.
I am tired. That's all, no more explaination. I guess you were asked by your girlfriend why not pick up the phone.