Not all veterinarians treat hamsters. To prepare for a medical emergency it is advisable to find a vet in your area who treats hamsters before he/she gets ill.
Also keep in mind that 24 hour vets are a specialty service and often are harder to find and significantly more expensive.
If your hamster gets sick, immediately separate the hamster from any other animals, particularly other hamsters. This is a precautionary measure in the event the illness is contagious. The isolation area should be quiet, warm and draft-free to allow the ill hamster an opportunity to rest and recuperate in a stress-free environment. Keep close watch on any other hamsters, and if they show any symptoms set up another hospital unit, preferably in a different room.
Don't attempt to diagnose the problem yourself. Seek consultation with a veterinarian. Most vets have reasonable rates for hamsters. Never give a sick animal medications designed for other animals or over-the-counter drugs for humans. Obtain either a prescription from the veterinarian or administer other available drugs and medications in accordance with the vet's instructions.