Aubrey O'Day -- I Have Mental Health Issues

Aubrey O'Day is a certified headcase ... so says one of her doctors, who issued the reality star an official medical document which allows her to bring her dogs on to an airplane.

A rep for Virgin America airlines tells TMZ ... the "Celebrity Apprentice" star was cleared to bring her 2 pets into the 1st class section of a flight this week ... because they are registered as "Emotional Support Animals."

So how does one get emotional support animal clearance? Ya gotta have a doctor write a letter ... stating you have mental issues.

According to the Virgin America website, the airline requires the passenger to produce a letter from a licensed mental health professional which substantiates the guest's disability-related need for the animal to accompany them in the aircraft cabin.

V.A. claims the letter must state that the passenger "has a mental health-related disability" ... and that having the animal accompany the passenger is necessary for his or her mental health.

The nature of O'Day's mental health issue is unclear. We called the starlet for comment.

O'Day tweeted pics of the dogs enjoying themselves on the flight to San Francisco ... and the V.A. rep tells us she was "incredibly sweet and polite" ... and nothing short of a "great guest."