Which of the following is a severe sign of hyperkalaemia?

Flaccid paralysis is a severe sign of hyperkalaemia due to the critical impact high potassium levels have on muscle function and nerve conduction. In hyperkalaemia, elevated potassium levels can disrupt the normal electrical activity of muscle cells, leading to symptoms such as muscle weakness and paralysis. Flaccid paralysis specifically refers to a state where there is a loss of muscle tone and strength, which can be life-threatening if it affects respiratory muscles or other vital functions.

The other symptoms mentioned, such as mild muscle cramping, persistent headache, and increased urination, are not indicative of severe hyperkalaemia. Mild muscle cramping may occur with electrolyte imbalances but is not as serious as flaccid paralysis. Persistent headache can be due to a variety of factors and does not specifically signal severe hyperkalaemia. Increased urination is typically associated with other conditions and does not directly correlate with the severe muscle dysfunction related to hyperkalaemia. Therefore, flaccid paralysis stands out as a critical and severe manifestation of this condition.