The best thing to do is contact a Vipassana center in the U.S.. I don’t practice Vipassana, so I can’t recommend a good center, and I also don’t know what state you’re in. But here is a list of some centers in the U.S. by state. It’s for people to take courses, but you can contact the center directly to ask about retreats. I’ve sat many zazen retreats, and I would recommend that you try one of their courses before sitting a 5 day retreat. The dynamic at retreats can range from tranquil to painful to crazy. It’s important to have some knowledge of the group you are practicing with before you engage in your first experience. Said another way, after you do a 5-day retreat, you want to be able to ask yourself if you would do it again. But if it was a bad experience you won’t know if it was because you don’t like Vipassana or because you didn’t like that group. Good luck!