Joseph D. Emerson admitted to law enforcement he tried shutting off the plane's engines during a "nervous breakdown" in the cockpit, adding he felt dehydrated and tired and had not slept in 40 hours.

According to the criminal complaint, obtained by TMZ, Emerson told investigators, "I didn't feel okay. It seemed like the pilots weren't paying attention to what was going on. They didn't ... it didn't seem right."

Emerson copped to pulling both emergency shut-off handles, explaining ... "I thought I was dreaming and I just wanna wake up."

Police say Emerson told them he wasn't taking any medication, but said he had been depressed for about six months ... and then the conversation turned to psychedelic mushrooms.

The complaint says Emerson told investigators about his use of magic mushrooms, saying it was his first time taking shrooms. The complaint does not make it clear when or how many mushrooms Emerson ingested, but there's an insinuation he might have been on mushrooms during the flight.

As we reported, Emerson was arrested and booked on 83 accounts of attempted murder for the incident on a flight from Washington to San Francisco.

Now, the feds are charging him with inference with flight crew members and attendants ... a charge carrying a prison sentence of up to 20 years behind bars.

Remember ... the captain and first officer subdued Emerson in the cockpit after he tried to shut off the engines mid-flight.

The pilots told cops that before Emerson reached for the handles he stated, "I'm not okay."

The complaint says after Emerson was subdued, he told a flight attendant, "You need to cuff me right now or it's going to be bad." Another flight attendant says Emerson stated, "I messed everything up" and the attendant told investigators, "he tried to kill everybody."