I did the same thing. Lately I say a quick prayer and go back to sleep during the take-off and I found I was crossing myself in the theatre.
Felt different because my theatre seat was way more comfortable and roomy than an airliner seat!
Incredible how the cinematic techiques made one feel as if one was there, and not just watching.
The movie is great. Some complain that it is not artsy enough and characters not established, but I like it, because it is not about one particular person, its about Americans fighting with terrorists and effect of this movie is like nothing else. You have to see it.