Daily mermaid fact #742
Certain merfolk can go into a state of dormancy when temperatures become too cold to bear! When faced with freezing temperatures, a merson's movements first become sluggish and clumsy, and their thoughts become foggy. Their heart rate and bodily functions begin slowing down, and soon they will fall into a deep sleep. They tend to sleep for periods of a few days at a time, waking up for brief moments. Once temperatures warm up again, their metabolism picks up and they go back to normal living and a normal sleep cycle.
Hibernation was an important factor in the survival of the first cold climate merfolk. It allowed them to survive the hostile aquatic environment they were forced into, though nowadays hibernation is not recommended for health reasons if one can help it. Hibernation takes a toll on the body, causing stunted growth and weakened immune system function, and may even lead to a shorter lifespan in the long run.
While merfolk of colder climates with icy winters tend to be able to hibernate, others… may not. Merfolk that originate from warmer climates tend to die from hypothermia if exposed to freezing cold for too long, just like "normal" humans.