Unhealthy or “nervous” laughter comes from the throat. This nervous laughter is not true laughter, but an expression of tension and anxiety. Instead of relaxing a person, nervous laughter tightens them up even further. Much of this nervous laughter is produced in times of high emotional stress, especially during times where an individual is afraid they might harm another person in various ways, such as a person’s feelings or even physically.
https://en.wikipedia.org/wiki/Nervous_laughter