I have 2 guinea pigs about 3-4 years old and have noticed that both have become much slower. They always run at noise or if we move close (we adopted them from another family) but recently they just sit in one spot. They only want to go out in their run in the evenings and just appear much slower and not as responsive. They are eating and drinking and I am doing as much as I can to prevent them overheating. Advice would be great please