When a liquid, height or any sort of amount is dramatically reduced. Typically used in an Xtreme, or passionate manner of speech. In such a manner one might say "jacked up" but since the instance is referring to a lessening of amount "jacked down" is used (ant. jacked up.)(syn.lowered)
Dave: "Dude. M2 Dew Xtreme is some B2W (balls to the wall) shit. I slammed a 2 liter this morning nude surfsailing Satan's Chasm, but now this afternoon my blood sugar is jacked up."
Shane: "So your blood sugar is high then? It should be low."
Dave: "Ya, dude. I meant 'jacked down' (Dave winks at Urban Dictionary and reapplies zinc oxide to nose)".
Did you see the Governator speak at graduation? He looked so jacked down in person.