As far as I can remember I've never asked for a seat switch on the basis on "attachment" difficulties-although as my teenage son is on the autistic spectrum I would if I needed to however I've twice asked for a switch for other reasons.
First was on VS LGW to LAS when I was seated next to a POS. Very nice lady who was in the middle seat-her husband had the window and I had (almost half of) the aisle seat. The FA upgraded a guy sitting close to us onboard so I took a deep breath (didn't want to offend the lady next to me) and said if they were shifting around and an aisle seat came free perhaps she could move me into it as we were a little squished here. They complied.
The only other time was BD LHR to BHD. Had been allocated a window seat....not my preference but I reckoned for an hours flight I could live with it.....until I sat down and realised the poor chap in the middle seat next to me was a very nervous flyer and was in a complete state. There was quite simply no way I could stay next to him for the flight as he was visibly shaking and talking nervously non-stop. I'm not a nervous flyer by any means but he really freaked me out. Again I didn't want to make the guy feel any worse so simply informed the FA that I was slightly claustrophobic and had asked for an aisle seat and to please switch me if at all possible-which despite it been a full flight-they did.

So apart from the "I can't bear to be parted" scenario -have you ever asked for a seat switch for other reasons ? How did you handle it and did you get it ?