Thomson Flight 1714 departed Newcastle on Sunday, bound for Larnaca in Cyprus.
But passengers ended up in Sofia, Bulgaria, instead.
Just 16 minutes into the flight, the pilot collapsed in the cockpit.
Passengers said cabin crew rushed to retrieve oxygen cylinders to help the pilot.
One passenger told the Sun: ”It was terrifying. I glimpsed inside the cockpit door.
“There was coffee all over the floor and it looked like the guy had collapsed.
“He was lying prostrate on the floor. It’s not what you want to see happening at the front of the plane.”
The plane made an emergency landing in Bulgaria, where passengers had to stay in hotels overnight.
A new flight departed on Monday afternoon, bound for their intended destination in Cyprus.
Another passenger, who had spent more than £2,100 on a holiday, said: “Money wasn’t what I was thinking about when the pilot collapsed.
“He was wheeled out of the cockpit and off the plane after our emergency landing before being placed on a stretcher and taken off to hospital.”
Other passengers took to Twitter to request answers as to why they were in Bulgaria for the night.
One person tweeted: “Stuck @ Sofia airport after plane diverted from Newcastle… anyone know whats happening.”
Another said: “What the hell is going on, diverted to Sofia, trying to get home to Larnaca! 24 hour helpline ho help no flight info.”
Thomson confirmed the flight was diverted due to a pilot becoming ill.
A spokesperson for the holiday company said: “A priority landing was requested at Sofia, Bulgaria which was the closest airport and the pilot was taken to a nearby hospital to be assessed.
“We would like to thank all of our customers for their patience and we are working to get them on their holiday as quickly as possible.
“The welfare of all customers and crew travelling with us is our priority at all times.”
Last week a Ryanair plane was forced to divert to Stansted after a security scare on board.
