In water, a body loses heat 90 times as much as it does in air.
But humpback whales have been found sleeping on the surface for up to ½ hour.
On average, whales sleep for about 7% of their day, with the exception of beluga whales, who can sleep for up to 30% of their day.
Killer whales or orcas can spend anywhere between 5 to 8 hours sleeping.