I live in Florida and have many in my gardens. Impatiens are a really vigorous plant. I use a 6-6-6 fertilizer throughout my entire lanscaping with the exception of my palms...........flowers, rose bushes, crape myrtles, and even my fruit trees. Sometimes in the very heat of the summer I will turn on my irrigation first thing in the morning and water my lawn and landscaping about 20 minutes a day and everything looks gorgeous. When the rainy season begins in June I no longer water with irrigation and let nature do it's own thing. One thing the impatiens will do is wilt right down to the ground and look as though they need to be extricated from the gardens, I believe a combination of heat and lack of water. I turn on the irrigation 20 minutes and when I go back outside in an hour or so, they look fabulous again! Either ours needed water or maybe it's possible to over water them and drown the roots but if the climate was warm and humid, and they wilted to the ground like they were dead, they needed water!

I realize that this thread is over a month old but i just want to add. I want to say im pretty sure the main reason your impatiens has wilted is because you have given it way way way too much water. I apoligize if i am wrong, but you sound like a beginner to me,so i do understand since it is VERY common for people to overwater. shuckapeafarms, even though that experience would be helpful, i dont think it applies to the fall. Even though watering every day in the summer would be ideal, not in the fall/winter. If the soil keeps drying out then maybe theres something wrong, but if the soil is not a little dry to the touch when you water then you are drowning the poor plant! Also, if you are having frosts now, then your plant may be dying because of that, so you may have to just grow a new one next year!
Hope i help you and your impatien!