I'm so tired, I haven't slept a wink.
I'm so tired, my mind is on the blink.
I wonder, should I get up and fix myself a drink?
No, no, no.
You know the feeling: so tired your mind feels like Jello. You're not fit to operate a moving vehicle. Your vocabulary is reduced to mostly monosyllabic words, and you're certainly not much use at a keyboard.