The spiritual meaning of "sink" is relatively easy to see: It means to descend into lower spiritual states, especially into states where false reasoning and the desire for evil predominate. This can represent a permanent state for those confirmed in evil living in hell, and it can also represent states of temptation we all go through repeatedly, when our our desires to be good and our true beliefs from the Lord come under attack from the desire for evil and false reasoning. "Sinking," of course, often has to do with water. Water usually represents natural truth, or true ideas about day-to-day life. But in the reverse sense it can also represent falsity, twisted logic that assaults our belief.