Courtenay Semel is ready to stop lighting her girlfriends' hair on fire, or at least regain access to the trust fund her father, former Yahoo CEO Terry Semel, locked her out of.

She's headed to rehab, Page Six reports, using a cover her ex Lindsay Lohan would appreciate: Exhaustion, which Lohan used to claim crippled her on movie sets (before she was arrested for cocaine possession).

A rep for Semel tells us, "Courtenay has indeed checked into rehab . . . She's emotionally, physically and mentally exhausted.

There's no question this "exhaustion" bug has been going around; it sent Heather Locklear into an Arizona treatment facility last year, around the time Kirsten Dunst sought rehab for, uh, depression.

It's hard to tell what left Semel more tired out: Allegedly punching that security guard in Las Vegas, purportedly setting girlfriend and fellow heiress Casey Johnson's hair on fire (a charge Semel denies) or working on that reality show.

Actually, none of the above: Our money's on "trying to live for a month without access to daddy's money." Talk about exhausting.