Five questions people search at two in the morning, answered from the feline medicine guidelines and the published studies rather than from other websites. Each one separates what is normal from what is a reason to call a vet, because that is the part that actually matters and the part most pages skip.
The behavior management guidelines say to treat any underlying medical condition before starting on behavior. A cat that has recently started doing something it never did before gets a vet appointment first. That order is the whole point of these pages.
When a cat stops using the litter box follows the same rule. The symptom checker asks what you are seeing and tells you whether it waits until morning. The senior checkup covers what should be tested and when.