Yes, you CAN sink in it, especially if you have small feet or are 'above average' in weight.
Not very far, though, but up to your family jewels at least, if you're stupid enough to try to walk on the stuff.
Also, you'll probably sink a bit more slowly than if you tried to walk on water, engine oil, or cetchup...
Lie down on your back, and yes, as long as your alter ego is AsbestosMan, you have a good chance of surviving.
(Pity about that cough, though. )