Quicksand is hardly the soupy stuff shown in the movies. It looks pretty solid and may be solid for a little bit. That is, until you happen to step in it and *SPLOCK*, you are are stuck fast rather than finding yourself being pulled down to the bottom of a tank in a second-rate movie set. We could go into all sorts of explanations about liquifaction with all kinds of meaningless equations, but just be aware that quicksand is like wet stucco and you are the stuckee.
Assuming you are not dead yet and can still read your laptop or phone screen, we advise you to wait for assistance while energetically screaming your head off. This will attract the nearest large predator, maybe even a grue, who will bite down on your head to pull you out of the muck. Don't struggle since you might end up pulling your rescuer in with you. Make sure you explain that you want your head back after the effort and that you will gladly give up all your energy bars and other food for their help. If the creature merely bit your head off and took off with it, you might try to advertise on Craigslist to get it back.