This has only happened to me with a couple of clients - it's been younger ones who've probably seen it in porn 
I've just said "Don't press on my throat please darling, it's not safe" and they've stopped.
Guys REALLY shouldn't do this without asking.
I had one who , because of the really bad reception in the hotel was a no show , so I went to the bar , to eat and get a drink .
My phone rang once I left the room and he was in the bar calling me , finishing a pint , I'd changed and realised so I apologised and offered to buy him a drink .
I don't drink on bookings or take drinkers and don't work at night so I'd given him plenty of time and had finished about 7ish .
Anyway he necked his pint in about 5 secs , so I guessed as he grumbled he'd been there ages about 40 mins he'd had a few .
I showed him my phone to prove I hadn't got his messages and he kept making jokey ( in hindsight passive aggressive comments)
Anyway I was pretty new and during he grabbed both my wrists and held them down, hard like Chinese burns, saying I bet you like this , I felt him loosen his grip and thought shit he's going to put his hand over my mouth , so I managed to get my knees up on his chest and really told him off, he said he was joking . I didn't understand this site properly ( still don't)then .
He was a horrible man , next day got a message from him wanting to book again that day but my messages wouldn't send..so I went outside to get a reception and had about five messages saying I was a time waster and lots of other stuff.
I won't let anyone go near my neck , husband anyone ,even children for personal reasons ..it's my main biggy it freaks me and blindfolds ..even my leather spikey chocker makes me feel weird but it looks cool lol so I can cope
But VC what a lovely , polite way to say it and firm .