To dream of plunging into something is to recognize that we are facing uncertainty. We are going into something unknown – something that we have perhaps not done before – and are taking a risk.
That risk will very often take us into our emotional depths and we will learn new things about ourselves, of which we will then be able to make use.
The sports of bungee and parachute jumping epitomize this. You may like to consult the entries for diving and plumbing.