Its always best to get professional diagnosis. Its true that they don't really show illness it wasn't until my 6 yr old female started to have seizures that we knew something was drastically wrong with her. It was hindsight that we started to see changes in her food intake, withdrawing from people till it was to late. Its really for the best that you take your kitty to the vet from one feline Mom to another play it safe it could be nothing.
I really don't want you to have to go through the same as I did and lose your best friend.