Summarize the following:
The room temperature should be around 20°C. Wait for 2 - 3 days. If the hamster is merely hibernating it should wake within that period.   If it doesn't wake up, then more obvious signs of death should occur such as an unpleasant odor and rigor mortis. A hibernating hamster should not smell unpleasant. Experts advocate this as the preferred option of waking a hamster because it closer simulates the natural waking process and places less strain on the body's blood glucose reserves than a "rapid reboot." Make sure plenty of food and water is available for the waking hamster. Instead of warming up your hamster slowly in a warm room, you can warm it more rapidly. Put the hamster, in its cage, in a warm place such as an airing cupboard. Depending on the temperature, the hamster may wake within 2 - 3 hours.  Remember to keep the hamster in a secure container, because if it is just in a cardboard box it may wake and chew its way out! Another idea is to stand the cage on a hot water bottle to radiate heat up through the floor of the cage. Ensure the hamster has food and water, because it will use up valuable energy reserves to wake up, and these need to be rapidly replaced or the hamster could suffer liver damage. If your hamster was hibernating, be aware this is a natural process, from which it recovered. Unless you are concerned, if the hamster is back to hits usual self - eating, grooming, and running in its wheel -  there is no specific need to get it checked by a veterinarian. If none of your attempts help to wake the hamster up, it has probably passed away. Remember that hamsters generally have very short lives and their time might unfortunately be up. Eliminate all other possibilities first, but then you may need to accept that your hamster has died. So that you don't have to suffer this anxiety and worry again, make sure the hamster is always in a room above 20°C, that he has 12 hours + light a day, and plenty of food and water. That way his body never thinks he has to conserve energy and hibernate.

Summary:
Put a hamster that you suspect is hibernating in a warm room. Warm the hamster up, relatively rapidly. Remember that hibernation is a natural process. Remember that hamsters have relatively short lives. Prevent the hamster from hibernating in the future.