There is a very specific fear that you will lose control of your own mind. You worry that the anxiety will become so intense that you will snap. You fear you might scream or try to open the door or simply go mad. It feels like a possibility because the fear is overwhelming and you feel trapped.
This fear often comes from a history of having your emotions invalidated. If you were gaslit as a child or told that your reality wasn't real then you might doubt your own sanity. You might feel that your mind is fragile. The truth is that fear is an adaptive mechanism. It is your system trying to protect you. It is alerting you to potential danger. It is not trying to destroy you.
No one has ever "gone crazy" just from being afraid on a plane. You might feel intense panic. You might cry. You might shake. These are normal reactions to high stress. They are not insanity. You have a "window of tolerance" for stress. When you leave that window you feel overwhelmed. But you always come back. The human mind is resilient. You have survived every bad day you have ever had.
You can ground yourself in the moment. Remind yourself: "I am feeling fear. This is a chemical reaction. It is temporary." You are not your fear. You are the observer of your fear. The sensation of "losing your mind" is just a sensation. It is not a prediction of the future. You will land. You will walk off the plane. You will still be you.