Hi, Depressed-Fiance, and welcome to Psych Central! Is your girlfriend mentally ill? Why would she act the way she did and try to choke you?
I can understand your wanting to defend yourself, especially if you are being choked. I think most folks would have fought back. However, I am very concerned about your relationship getting physical. Anything like that will get worse after marriage, I think.
I do suggest the two of you go into some pre-marriage counseling. I hope your girlfriend will also get some personal counseling.
Please try not to worry about what happened. I think the thing to be concerned about is the future. Okay?