[[Airline]]s and other travel companies often require passengers to provide evidence that they are medically fit to fly, particularly if they have a medical condition that may affect their ability to travel safely.

The specific requirements for being "fit to fly" can vary depending on the airline or travel company, and may also depend on the destination and duration of the flight. In general, passengers who have recently undergone surgery or who have a medical condition that may affect their ability to sit upright for extended periods of time may need clearance from their doctor before being allowed to fly.

Certain medical conditions may also require additional medical equipment or accommodations during the flight, such as oxygen tanks or specialized seating. Passengers with these conditions may be required to provide a medical certificate or clearance from their doctor in order to fly.

It is important for passengers to be honest and upfront about any medical conditions or concerns they may have when booking their flight. This can help ensure that appropriate accommodations are made and that the passenger can travel safely and comfortably.