Death by fatal hilarity is usually brought about by two means:
Asphyxiation, from which the thoracic diaphragm can't expand or contract fully thus causing the inability to breathe correctly. One of the main processes of laughter involves the continuous expansion and contraction of the thoracic diaphragm, bringing in and releasing air into and from lungs. It is possible to overexert and strain this muscle to where it becomes too weakened to perform normally. Other lung conditions such as asthma, bronchitis, hypersensitivity pneumonitis, Acute Respiratory Distress Syndrome (ARDS), and many others may become agitated and contribute to death.
Heart failure, heart attack, and cardiac arrest are the most common of heart conditions that are likely to occur due to constant straining on the heart, ultimately preventing blood flow. As a person laughs, their heart rate increases above the normal ranges. However, as laughter continues, the heart rate may reach dangerous levels that the heart isn't accustomed to, straining and damaging it. Other heart conditions include coronary heart disease, cardiac arrhythmia, ischaemic heart disease, and others can also be affected.
