AJNAG, when transplanting some people advise to water the plant first, wait about five minutes or so, then do the transplant After transplanting, water it in its new pot. The reason is because sometimes when transplanting with dry soil, the flow of water from the roots to the leaves might be interrupted. If the flow of water is interrupted, wilting can occur. Personally, I've never had a problem with transplanting, either dry or wet, but I always water first now.
Your plant is probably experiencing some sort of transplant shock, and I imagine it will recover over the next few days or so.