A leech is a parasitic bloodsucking worm often living in freshwater. In the past, leeches were used for surgical reasons to remove impurities in the blood and treat diseases.
Positive: Dreaming of a leech sucking out a disease could represent the Lord cleansing you of your impurities. It could also represent God sucking your anxieties or pressures out of your body and restoring you.
Negative: Seeing a leech in a dream may represent the type of sin that sucks the life out of a person spiritually. It could also represent never being satisfied or never having enough.
(Proverbs 30:15; Romans 12:2; Jeremiah 33:6).