You can absolutely fall from grace. What do you think this is a warning of?...No what I am saying is that I don't think you can fall from Grace. If you were truly saved then you would stop your sinful ways. However, since we are not perfect we will definitely sin again that's when you should turn to pray and seek forgiveness.
20 For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.
21 For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them.
22 But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire.