Fluid plugs as downhole sealing devices and methods include providing a stimulating fluid to a casing conduit that is defined by the production casing to stimulate a portion of a subterranean formation within which the production casing extends. The methods further may include providing a sealing fluid to the casing conduit, providing a sealing device to the casing conduit, and flowing the sealing fluid and the sealing device to a perforated section of the production casing. The methods further may include locating the sealing device on a perforation, generating a fluid plug within the perforated section of the production casing by increasing a viscosity of the sealing fluid, and retaining the sealing device proximate the perforation with the fluid plug.