auto-immune diseases
the immune system is supposed to detect and neutralise foreign bodies but it can turn on the dogs own cells. it can be genetic (inherited or mutation) and can be invoked by vaccine reactions.
it basically kills the dog from the inside out.
these can include anaemia (which is a symptom, not the disease) where your iron / red blood cell / oxygen transport doesnt work properly. become tired easily, lethargic.
ETA: hey you … i was typing stuff out – do we just guess the condition first ?? !!!
claire x