Wikipedia path: Virus -> Immune system -> Innate immune system -> Parasites -> List of parasites of humans -> Naegleria fowleri -> Primary amoebic meningoencephalitis -> Deciding I DEFINITELY shouldn't connect an aquarium pump to my sinuses
This pie chart for the most part reflects the usual experience of being sick — tossing and turning in bed and cleaning up mucus and other bodily fluids from facial orifices— in addition to a few ponderings of a rather more scientific bent.
The "army of critters that patrol my body" would appear to refer to the human immune system, which is made up of various cells and processes that actively fight infections and pathogens.
The punchline appears to be "pondering hooking an aquarium pump to my sinuses," which indicates that Randall's sinuses were completely clogged with mucus, which made him wonder whether hooking up an aquarium pump would help clear them out, perhaps akin to a Neti pot. Studies on nasal irrigation, however, have had mixed results, and the practice may not in fact be beneficial.
Randall's Wikipedia path: Virus → Immune system → Innate immune system → Parasites → List of parasites of humans → Naegleria fowleri → Primary amoebic meningoencephalitis.
Naegleria fowleri is known as the brain-eating amoeba. It is found in warm bodies of stagnant fresh water and causes the disease primary amoebic meningoencephalitis, a rare but highly lethal condition. Although N. fowleri are not commonly found in aquaria, Randall's Wikipedia wanderings force him to conclude that attempting to clear out his sinuses with an aquarium pump is too risky. Since this danger would presumably not be present at all with an unused, sterilized aquarium pump, the comic may be referring to a particular pump currently in use and close at hand.