Cackle Fever

This horrifying disease causes afflicted humanoids to frequently succumb to fits of manic laughter, which gives the disease its morbid nickname: "the shrieks". This disease spreads through the laughter that is produces during periods of stress. Any creature within 10 feet of a stage 3 victim is exposed to the disease through the air. The laughing allows its offspring to float on hurled droplets and ride the wind to their next host. 
Any humanoid exposed to Cackle Fever must succeed on a DC 13 Constitution saving throw or contract the disease at stage 1. While infected, the creature must repeat the saving throw once every 24 hours. On a successful save, the creature's condition decreases a stage. If they fail the save, the condition progresses a stage. If the creature successfully saves while on stage 1, the disease is shaken off and they are no longer infected.

Type

Parasitic

Stage 1
The infected creature begins to run a fever and feels disoriented. This gives it one level of exhaustion that cannot be removed until the disease is cured. 
Stage 2
The trademark symptom begins during this stage. Whenever the infected creature is in a situation that leads to an increase of adrenaline in the bloodstream, they must succeed on a DC 13 Constitution saving throw. If they fail the save, they take 5 (1d10) psychic damage and are incapacitated due to manic laughter for 1 minute. 
Stage 3
This stage does not have any notable effect in the afflicted, but they are able to transmit the disease to any humanoid within 10 feet of them when they have a laughing outburst.