Following on from what svengali said about this, even with a trustworthy partner there are a lot of risks involved.
Precisely because it sneaks up on you and also because of the enhancement in arousal for some, there is a very real risk that things will be pushed too far before anyone is aware there is a problem. There have been a number of situations over the years where the person being strangled/choked has encouraged the person doing that to keep going only for that to prove to be too much. Furthermore, particularly if it is a couple where one enjoys performing the strangulation and another enjoys receiving it, there is a high likelihood of getting lost in the throes which can mean that those involved aren't paying attention to what's happening.
My advice for anyone wanting to try this is to visit a professional with training in B&D/S&M who will make the experience fantastic while also retaining control and awareness of how the person being strangled is handling the situation. If doing it in a personal situation, always have a safe word and don't go too far the first few times until you are aware of your limits.