Afterward Jesus findeth him in the temple, and said unto him, Behold, thou art made whole: sin no more, lest a worse thing come unto thee. John 5:14
Once Christ has healed and made us whole, if we turn back to our old ways—even if just one tiny minute way—we are turning back to that which Christ delivered us from (sin, disease). We have turned back to our vomit. A worse thing will come upon the soul that does this. Because God spoke it, His word comes to pass. Period.