O que significa I have to rev myself up ?

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It means that the speaker is either sleepy, tired, sore, sick, scared or for some other reason doesn't feel ready to do something, and to rev/revving myself up means to get oneself prepared through some means other than a slow natural process.
Ex. "I was sore before my football game, so i revved myself up with some exercise"
"I didnt want to wake up this morning, but i revved myself up with some coffee"
"I was scared of sky-diving, but i revved myself up with some music"
Revving oneself up might also be purely psychological, and not require any physical aspect.
It is not a common expression, and is very casual, but athletes, soldiers, or fighters might use this phrase more regularly. The phrase comes from the word revolution, and was first used to describe the act of increasing the speed, or "revolutions per minute", of an engine.