Selma Blair's service dog was along for the wild plane ride that ended with the actress in handcuffs ... and while Selma is in the hospital, we're told her four-legged companion is doing just fine.

Sources tell TMZ ... Selma's English Red Fox Labrador, Scout, was aboard Sunday's Delta flight when the actress allegedly went berserk on the crew. We're told Scout is safe and was picked up by Selma's lawyer at JFK Airport.

Selma got Scout in 2021, three years after revealing her multiple sclerosis diagnosis.

TMZ broke the story ... Selma was arrested after allegedly punching one flight attendant and biting another while the plane was in the air.

Things apparently went from bad to worse once the plane landed ... we're told Selma repeatedly kicked a Port Authority police officer in the head while riding in an ambulance, then allegedly assaulted a nurse at the hospital.

She's now facing 2 assault charges ... one involving the officer and another involving the nurse.

We also obtained audio capturing Selma screaming as she exited the plane ... while dispatch audio revealed she apparently bashed her head against a bulkhead during the ordeal.

A rep for the actress told us she suffered a medical emergency that led to the alleged behavior, and she's now in stable condition.

Law enforcement sources tell TMZ ... The FBI issued Selma a federal summons charging her federally with "assault within the special maritime and territorial jurisdiction of the United States."

Woof.