Overdrive is when you get hyper-active due to being over-tired, over-worked, or over-stressed. Common symptoms include slurred or incoherrent speach, laughing histerically over stupid things, and improper brain function, while in a sober state.

A term used to reference cannabis/marijuana/weed.

You know you're in overdrive when you haven't had any sleep in a long time and suddenly your fatigue is taken over by this crazy ass energy that makes you act stupid.

When you go above and beyond the usual limits.
One of my favourite examples is in Final Fantasy X where each character's most powerful abilities can only be done in Overdrive.
See overclock

When you're about to cum but the woman chomps down on your cock, making you eject both blood and semen at the same time. This causes a chemical reaction in which you get a throbbing sensation running down your now flacid penis and it feels like you are ascending into overdrive.

The paradoxical state where you're super tired, but at the same time, you've got a lot of energy.