The Land Rover hit a white van and a red Seat, which smashed through a wall and landed on the bonnet of a silver BMW X5, at Warwick Hospital.
The driver of the Land Rover was taken into the hospital to be treated after the accident at 16:20 GMT on Wednesday.
A West Midlands Ambulance Service spokesman said: "Thankfully no-one else was injured in the crash."
Hospital staff ran into their own car park to treat a driver who fell ill at the wheel and crashed into three cars.