Hmm, I've recently (as mentioned in another thread, which I really need to reply to and thank the contributors) started experiencing panic attacks, one of which was in a similar situation to the one which you describe. Having spoken to a couple of other panic attack sufferers, this appears to be a 'danger spot' for air travel. So no, it's not so unusual.

As I understand it, one common thing with panic disorders is that there are a number of specific situations which can trigger a panic. Don't necessarily believe that it's rational (although it's easy to rationalise such an event), as it often isn't. Even if not agoraphobia, it's often like a form of claustrophobia. Only here, it's not so much a question of being enclosed, but rather being in a situation where you know there is no way to 'the outside' (you have left the ramp) and where you don't know what's going on (you can't really see, or it's dark) and you don't know how long you're going to be in this situation for.

In my, and my friends', cases, this can trigger irregular breathing that leads to hyperventilation and panic. All very unpleasant.

Now, this is personal and shared experience, and may not be in the slightest related to yours. However, I would ask:

Are you sure the panic is down to rational discomfort and not irrational fear?

Do you experience panic in similarly confined situations elsewhere in life?

Are you going through a period of high stress or similar pressure in your life?

Is this causing you major discomfort?

If it's causing you problems, you may want to see a doctor about it, even if it's just to make your flights less unpleasant and anxious.