unfortunately

When I'm on flight I like to sleep, but unfortunately I can't always sleep.

When something is unfortunate, it is unlucky. Here are some examples:

1. We were planning to play baseball, but unfortunately it started raining.
2. Unfortunately, I didn't get the job I was hoping for.

passing out

I had a bad experience drinking beer and then passing out on an airplane before.

Passing out means to lose consciousness. It is similar to falling asleep but it is usually caused by drinking too much or from a sudden fear or sickness. Notice the following examples:

1. He always keeps drinking until he passes out.
2. I can't stand the sight of blood. If I see it, I'll probably pass out.

concentrate

I'm too excited when I'm on a flight to concentrate on the movie.

When someone is concentrating, they are paying attention carefully. Here are some additional examples:

1. I can concentrate better on my work if I listen to music while I'm doing it.
2. It's hard to concentrate during that class because it is so boring.

complimentary

If there is any complimentary food or drink items, bring them to me.

Complimentary means that you don't have to pay for it. In other words, it's free. Here are two more examples:

1. At most hotels these days, the soap and shampoo are complimentary.
2. Conferences usually have a lot of complimentary promotional items.

passenger

I talk to the passenger next to me.

A passenger is a person who is riding on a bus, plane, train, car, boat or any moving vehicle. See the following examples:

1. He was sitting in the passenger seat when the accident happened.
2. Many of the passengers started to complain because it was so hot in the airplane.