At least for me there's a feeling of autonomy. If a plane crashes, there's very little that I as a non-superman can do to stop that from happening (with me inside it.) While driving, I can trust my own reflexes, awareness, and decision making to put myself in better or worse situations. Now this may still absolutely be a false perception, but this is where the feeling is rooted for me (from lengthy introspection on similar situations when I used to do trick-skiing and never really questioned my safety, but would be very hesitant to e.g. skydive).

To some degree I think it's potentially also "failure magnitudes." Having been in a handful of very minimal car crashes, that calibrates my "something goes bad" prior to a not very impactful bar; whereas if something goes wrong on a plane, it can go VERY VERY wrong. Again, this is likely a false perception due to observations of outlier events in both cases and sparsity of signal, I'm just trying to question the origin of my feelings.

There's this thing that will happen to me when I doze off as a passenger in a car: When I wake up, there's often a split second of panic between the visceral understanding that I'm in a moving vehicle and the slightly delayed recollection that I'm not the one responsible for driving it.

Somehow, this turned into a problem for me when flying (even though I'm not a pilot). I wake up, I instantly know I'm moving at 500 miles per hour through the air, then I have a singular panic of being in a vehicle not under my control. This has only happened once – I haven't slept on a plane since.

Speaking of irrational, when flying I think, "What if this is the day I discover my superpower to walk through objects and fall to the earth." I think that's about as irrational as I can get for a fear.

Curious phobia! Do you imagine yourself disintegrating on the surface of the earth or do you continue to fall through it?

Hah yeah. I have no idea why I think of that in planes. I assume it would even be worse on ground level, fall into the bedrock and never come back up.

It must be something from my childhood and stories or TV shows, and just stuck with me. I know I had recurring dreams when I was young, a futuristic belt that let me jump through walls, but detected and kept me on the floor without falling through.