Suppose f: M--->N$f: M\to N$ is a smooth map between two smooth manifolds, with M$M$ compact and connected, and suppose there is a dense subset of f(M)$f(M)$ where each fiber is connected, then each fiber of f$f$ is connected.
If it helps, you can just consider the case where the set of regular values is dense in f(M)$f(M)$ and the fiber of each regular value is connected, and you want to prove every fiber of f$f$ is connected.