As a pax I have experienced being sat next to someone with learning difficulties on a flight from London to Aberdeen.
Hubby was in the window seat, me in the Centre and the young man with difficulties in the aisle seat.
As soon as we sat down I realised all was not right as he was talking to himself. Then when I heard/saw him keep repeating "oxygen masks" and pointing to where they appear from I became quite alarmed. Then he kept saying "crash" and would then point to the emergency exits. This was before we had even taken off.
I became quite unsettled as I am not the best of flyers. I really didn't know what to do and whether I should speak to CC and ask to be moved.
As we taxied for take off he became worse. He kept expelling wind from his mouth as well and kept saying "shouldn't have eaten all that" so I then thought he was going to be sick.
Then we were back to "crash crash" By now I was leaning on hubby with my ear pressed firmly on hubby's chest and my hand on my other ear so I couldnt hear what he was saying.
The saving grace (for me) came when drinks were served. He had a can of coke and then decided he needed the toilet. In trying to get out of his seat, he leaned back so hard there was an almighty crack and a scream from behind. Yes he broke his seat and showered the lady behind with hot coffee.
As a result he, along with the 3 pax behind us, all had to be moved because of the broken seat.
An awful situation though as in a way I felt sorry for him but he made me very very anxious and uncomfortable.