This is "Created Equal" by Ken Jenks.
A college kid, who's volunteering for an experiment, gets his mind copied to everyone in the world:
I sat up in the chair. "Okay, Doc. Let's go." The sequence started
and I pushed the buttons as they lit up. Four minutes later, the
sequence ended. I unstrapped and said good-bye through the intercom. I
thought it was a little odd that I didn't get a response. Shrugging, I
ducked out to the bike rack, unlocked my rusty ten-speed and rode back
to our apartment on Gregory. Traffic was weird. There were a whole lot
of people running, driving and riding toward the Beckman Institute,
and there were even more headed in the same direction I was.
My apartment building was surrounded. There must have been three
hundred people there calling Katie's name. She peered out the window,
surveying the crowd, looking like a princess in a tower.
I made my way through the crowd, which parted around me. They started
calling my name, too. There was no pushing or shoving, and nobody was
being rude. It was like a dream. An hallucination. Too little sleep, I
thought. And I've got to cut down on the Mountain Dew.
The stairway was packed, but they let me through. When I opened the
door, the nearest people tried to come in with me, but stopped when I
told them to back off. Weird.
Katie was waiting. She looked odd, nervous. "Hi," she said. "Are you
"Yes," I said, "as far as I can tell."
"So am I," she replied. "I think Dr. K's telepathy experiment did
something weird. I have your brain in Katie's body."
Planes and surgery is mentioned explicitly:
There was no major loss of life. There were a few trucks that went out
of control. I never learned to drive a semi. An embarrassing number of
helicopters crashed. Thank God I can fly fixed-wing aircraft. Almost
all of the planes landed safely, even the big jets. There was a major
chemical leak at a refinery in Louisiana, but they seemed to get
everything under control quickly enough. Dozens of people around the
world died in surgery. My soul felt bruised, knowing I died so many
times. Newborn babies struggled with unaccustomed mouths to ask their
mothers about Katie and Dr. K.
The girlfriend becomes the leader:
Katie grabbed the megaphone. Everyone stopped and looked at her. Who
appointed her leader? I thought. I did, I guess.
The first chapter of the story is available via the wayback machine. The website where you could buy the whole story seems to have folded back in 2002, so you read it in the nick of time. I myself only ever read the free first chapter.