My hamster was breathing really fast, not really eating, curling up into a ball in corner of cage?

Diarrhea: Not all hamsters who suffer diarrhea, will have wet tail. The most common cause of diarrhea in hamsters is the overfeeding of fresh vegetables. Unlike Wet Tail, there is not loss of appetite or decreased activity; for the most part the hamster will appear as normal.

Do not let diarrhea stay for prolonged periods of time, as dehydration becomes a big concern. You will want to withhold fresh foods for a few days and resume only if the diarrhea is completely resolved; you can start giving fresh produce again but slowly. Skin Diseases: Mites, ringworm, allergies, and skin infections, are the most common skin illnesses associated with hamsters.

Watch for flakiness or redness of the skin, hair loss, lesions on the skin, or if the hamster appears to be scratching more. In these cases you will want to see a vet to determine the exact cause of the skin concern. Pine and cedar bedding can cause skin irritation, as well as, lung problems, so avoid these beddings.

Hibernation: Watch the room temperature where the hamster's cage is. If the temperatures fall below normal, the hamster may go into a hibernating state, where they can appear very still and breath slowly. Your hamster is not dead or dying, in this case, but you will want to rewarm the hamster.