unconscious
Explanation
The Joke
A woman is telling another couple about a frightening experience with her son: "When I looked down, your son was unconscious and his breathing was barely detectable and his temperature was dropping and his pulse was slowed and his eyes were darting around like crazy!" In the next panel, someone asks "Where is he now?" and the mother calmly replies "Sleeping, like I told you." The final panel shows the couple exasperated, with the mother saying "Get it?!"
The Humor
The entire joke hinges on the misdirection between medical emergency and perfectly normal sleep. The woman describes her son's condition using alarming clinical language -- unconscious, barely detectable breathing, dropping temperature, slowed pulse, darting eyes (REM sleep) -- which are all technically accurate descriptions of a person who is simply asleep. She is clearly delighted by her own cleverness in reframing ordinary sleep as a terrifying medical scenario, while her audience is understandably frustrated by the pointless alarm. The humor plays on how medical or scientific terminology can make completely mundane phenomena sound terrifying, and on the particular personality type who finds this kind of pedantic wordplay hilarious while everyone around them does not.