Personally, I get the feeling of cement feet. There's nothing really wrong. You like the people and you're good at the job, but it's not what you really want to do. Another symptom is when the balance of work versus outside activities is out of kilter. For some people, their outside lives start to take over.
Some jobs have predictable cycles.
If your visceral response to the cycle coming around again is depression, fatigue, or listlessness, you've gotten your first clue that it's probably time to get out. To know if you are still in the right job, you need to understand what is really important to you. I've always told people who have been fired that the most important thing they can do is take a holiday. Do this even if you have a job. Changing jobs can be hard.