This helpful handout from one of my veterinary journals helps to set the record straight on some common misconceptions about cats:
1 - Cats are aloof and antisocial
2 - Indoor cats don't need preventive health care
3 - Cats are independent and don't need medical care
4 - Cats eliminate outside of litter boxes out of spite
5 - Cats don't get heartworms
The only one of these which carries a grain of truth with it is the last - in Southern California, heartworm disease is uncommon enough that its incidence in local cats probably approaches zero, but given the big unknown of coyotes as a heartworm reservoir, that may be incorrect.
Anyway, click on the embedded link at the start to read the information sheet. And then call us to get that very overdue routine exam taken care of!