I don't know if it is any comfort, but the nonsense you see in films about people sinking into quicksands until you vanish is simply not going to happen.
The human body has a density a trifle less that of water in which you will float. Quicksand or mud will have a much higher density than that and you will float quite well in it.
The danger is that your legs will sink into it and you will get stuck. You may then be delayed long enough to be cut off when the tide comes in and that is, of course, bad News
If you DO get your feet stuck, then the trick is to lie down and roll yourself to firmer ground. Messy, but it will work. You will certainly not sink without trace.