How can I force my body to let me take shots?

I started drinking about a year ago, and everything was going good until about December of last year. I went over to a friend’s house, had 8 shots of Vodka and 2 beers, and then got in their hot tub for about an hour. I ended up blacking out, and threw up multiple times. I woke up the next day and threw up again several times. Since then, if I catch even a whiff of alcohol, I have a Vietnam flashback and have to stop myself from throwing up. I’ve taken less than 5 shots since that night. A few nights ago, my friends wanted to have some drinks again. I had a small sip of whiskey, which was a good start, but then I tried to take another shot of vodka, and my body just wouldn’t let me. I need to be able to drink with people again in the near future, how can I just get over this lingering memory of one bad experience and start taking shots normally again?