This can result from the break-up of a relationship, trouble within the family or the death of someone close to you.
It may involve drug use.
The term derives from the cruise control system on a car, which allows a specific speed to be set and regulated automatically by an onboard computer; the driver does not have to use the accelerator pedal
(Pun meaning the driver is "cruising" in the car, while the passenger is "controlling" the driver's penis)
Friend: "Dude, what took you so long to get here?!"
You: (Spoken in a sarcastic manner) "I was on cruise control the whole way here."