The type of mat that a chin gets from getting its entire body wet can be very hard to get out. Sometimes the only thing that can be done for that is to give very frequent dust baths and then slow removal of little bits of the mat here and there. Small amounts of fur will come out of it.
I had a chin a couple years back that had a huge mat on her back, it took six months to get it all out. Small mats aren't a problem, they usually slide right out. The really large ones require special care and attention.
Critical care would be a great idea right about now along with some Phazyme or simethicone containing product. Stress can take down a chin very quickly, it seems like the stress always seems to cause digestive issues.