I usually stay out of the benadryl discussions because it seems to always get heated. I always bring benadryl with, mostly because my DD does have a severe food allergy, but also for a sleep aid in an "emergency" situation. Not so much for the plane, but definitely for the hotel. We had a horrific experience at a hotel when my DD was just under a year old. She went to sleep fine, but woke up around 1am and, despite our best efforts, we could not get her back to sleep for 4 hours (and at that point, only with the help of benadryl). I think she realized that she wasn't at home and wasn't very happy about it. We tried everything...tons of nursing, walking, rocking, anything we could think of it, but she wouldn't go back to sleep. Finally, after about 3.5 hours, when DH and I were practically in tears from desperation, we gave her benadryl. She fell asleep shortly afterwards. Honestly, at that point, I thought that it was in everyones (my DD, me, DH, and the other hotel guests) best interest to give her the meds.
I just want to point out that this wasn't our first experience with Benadryl for our DD. When she was somewhere between 6 and 8 months, I would guess, her doctor told us to give her 2 ml of benadryl at night when she had a respiratory infection (she had several of those around that age). I thought we were giving it to her as some sort of decongestant or something, but the nurse at the ped's office said that it was actually to help her sleep (her coughing was waking her up). I'm not saying that this was right or wrong, and god knows I don't always agree with our pediatrician, but it was what she recommended for our DD when she was a baby.
I just want to point out that this wasn't our first experience with Benadryl for our DD. When she was somewhere between 6 and 8 months, I would guess, her doctor told us to give her 2 ml of benadryl at night when she had a respiratory infection (she had several of those around that age). I thought we were giving it to her as some sort of decongestant or something, but the nurse at the ped's office said that it was actually to help her sleep (her coughing was waking her up). I'm not saying that this was right or wrong, and god knows I don't always agree with our pediatrician, but it was what she recommended for our DD when she was a baby.